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PERLTODO(1)                           Perl Programmers Reference Guide                           PERLTODO(1)



NAME
       perltodo - Perl TO-DO List

DESCRIPTION
       This is a list of wishes for Perl. The most up to date version of this file is at
       http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod

       The tasks we think are smaller or easier are listed first. Anyone is welcome to work on any of these,
       but it's a good idea to first contact perl5-porters@perl.org to avoid duplication of effort, and to
       learn from any previous attempts. By all means contact a pumpking privately first if you prefer.

       Whilst patches to make the list shorter are most welcome, ideas to add to the list are also
       encouraged. Check the perl5-porters archives for past ideas, and any discussion about them. One set
       of archives may be found at:

           http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/

       What can we offer you in return? Fame, fortune, and everlasting glory? Maybe not, but if your patch
       is incorporated, then we'll add your name to the AUTHORS file, which ships in the official
       distribution. How many other programming languages offer you 1 line of immortality?

Tasks that only need Perl knowledge
   Improve Porting/cmpVERSION.pl to work from git tags
       See Porting/release_managers_guide.pod for a bit more detail.

   Migrate t/ from custom TAP generation
       Many tests below t/ still generate TAP by "hand", rather than using library functions. As explained
       in "Writing a test" in perlhack, tests in t/ are written in a particular way to test that more
       complex constructions actually work before using them routinely. Hence they don't use "Test::More",
       but instead there is an intentionally simpler library, t/test.pl. However, quite a few tests in t/
       have not been refactored to use it. Refactoring any of these tests, one at a time, is a useful thing
       TODO.

       The subdirectories base, cmd and comp, that contain the most basic tests, should be excluded from
       this task.

   Test that regen.pl was run
       There are various generated files shipped with the perl distribution, for things like header files
       generate from data. The generation scripts are written in perl, and all can be run by regen.pl.
       However, because they're written in perl, we can't run them before we've built perl. We can't run
       them as part of the Makefile, because changing files underneath make confuses it completely, and we
       don't want to run them automatically anyway, as they change files shipped by the distribution,
       something we seek not do to.

       If someone changes the data, but forgets to re-run regen.pl then the generated files are out of sync.
       It would be good to have a test in t/porting that checks that the generated files are in sync, and
       fails otherwise, to alert someone before they make a poor commit. I suspect that this would require
       adapting the scripts run from regen.pl to have dry-run options, and invoking them with these, or by
       refactoring them into a library that does the generation, which can be called by the scripts, and by
       the test.

   Automate perldelta generation
       The perldelta file accompanying each release summaries the major changes.  It's mostly manually
       generated currently, but some of that could be automated with a bit of perl, specifically the
       generation of

       Modules and Pragmata
       New Documentation
       New Tests

       See Porting/how_to_write_a_perldelta.pod for details.

   Remove duplication of test setup.
       Schwern notes, that there's duplication of code - lots and lots of tests have some variation on the
       big block of $Is_Foo checks.  We can safely put this into a file, change it to build an %Is hash and
       require it.  Maybe just put it into test.pl. Throw in the handy tainting subroutines.

   POD -> HTML conversion in the core still sucks
       Which is crazy given just how simple POD purports to be, and how simple HTML can be. It's not
       actually as simple as it sounds, particularly with the flexibility POD allows for "=item", but it
       would be good to improve the visual appeal of the HTML generated, and to avoid it having any
       validation errors. See also "make HTML install work", as the layout of installation tree is needed to
       improve the cross-linking.

       The addition of "Pod::Simple" and its related modules may make this task easier to complete.

   Make ExtUtils::ParseXS use strict;
       lib/ExtUtils/ParseXS.pm contains this line

           # use strict;  # One of these days...

       Simply uncomment it, and fix all the resulting issues :-)

       The more practical approach, to break the task down into manageable chunks, is to work your way
       though the code from bottom to top, or if necessary adding extra "{ ... }" blocks, and turning on
       strict within them.

   Make Schwern poorer
       We should have tests for everything. When all the core's modules are tested, Schwern has promised to
       donate to $500 to TPF. We may need volunteers to hold him upside down and shake vigorously in order
       to actually extract the cash.

   Improve the coverage of the core tests
       Use Devel::Cover to ascertain the core modules' test coverage, then add tests that are currently
       missing.

   test B
       A full test suite for the B module would be nice.

   A decent benchmark
       "perlbench" seems impervious to any recent changes made to the perl core. It would be useful to have
       a reasonable general benchmarking suite that roughly represented what current perl programs do, and
       measurably reported whether tweaks to the core improve, degrade or don't really affect performance,
       to guide people attempting to optimise the guts of perl. Gisle would welcome new tests for perlbench.

   fix tainting bugs
       Fix the bugs revealed by running the test suite with the "-t" switch (via "make test.taintwarn").

   Dual life everything
       As part of the "dists" plan, anything that doesn't belong in the smallest perl distribution needs to
       be dual lifed. Anything else can be too. Figure out what changes would be needed to package that
       module and its tests up for CPAN, and do so. Test it with older perl releases, and fix the problems
       you find.

       To make a minimal perl distribution, it's useful to look at t/lib/commonsense.t.

   Move dual-life pod/*.PL into ext
       Nearly all the dual-life modules have been moved to ext. However, we still  need to move pod/*.PL
       into their respective directories in ext/. They're referenced by (at least) "plextract" in
       Makefile.SH and "utils" in win32/Makefile and win32/makefile.ml, and listed explicitly in
       win32/pod.mak, vms/descrip_mms.template and utils.lst

   POSIX memory footprint
       Ilya observed that use POSIX; eats memory like there's no tomorrow, and at various times worked to
       cut it down. There is probably still fat to cut out - for example POSIX passes Exporter some very
       memory hungry data structures.

   embed.pl/makedef.pl
       There is a script embed.pl that generates several header files to prefix all of Perl's symbols in a
       consistent way, to provide some semblance of namespace support in "C". Functions are declared in
       embed.fnc, variables in interpvar.h. Quite a few of the functions and variables are conditionally
       declared there, using "#ifdef". However, embed.pl doesn't understand the C macros, so the rules about
       which symbols are present when is duplicated in makedef.pl. Writing things twice is bad, m'kay.  It
       would be good to teach "embed.pl" to understand the conditional compilation, and hence remove the
       duplication, and the mistakes it has caused.

   use strict; and AutoLoad
       Currently if you write

           package Whack;
           use AutoLoader 'AUTOLOAD';
           use strict;
           1;
           __END__
           sub bloop {
               print join (' ', No, strict, here), "!\n";
           }

       then "use strict;" isn't in force within the autoloaded subroutines. It would be more consistent (and
       less surprising) to arrange for all lexical pragmas in force at the __END__ block to be in force
       within each autoloaded subroutine.

       There's a similar problem with SelfLoader.

   profile installman
       The installman script is slow. All it is doing text processing, which we're told is something Perl is
       good at. So it would be nice to know what it is doing that is taking so much CPU, and where possible
       address it.

   enable lexical enabling/disabling of inidvidual warnings
       Currently, warnings can only be enabled or disabled by category. There are times when it would be
       useful to quash a single warning, not a whole category.

Tasks that need a little sysadmin-type knowledge
       Or if you prefer, tasks that you would learn from, and broaden your skills base...

   make HTML install work
       There is an "installhtml" target in the Makefile. It's marked as "experimental". It would be good to
       get this tested, make it work reliably, and remove the "experimental" tag. This would include

       1.  Checking that cross linking between various parts of the documentation works.  In particular that
           links work between the modules (files with POD in lib/) and the core documentation (files in
           pod/)

       2.  Work out how to split "perlfunc" into chunks, preferably one per function group, preferably with
           general case code that could be used elsewhere.  Challenges here are correctly identifying the
           groups of functions that go together, and making the right named external cross-links point to
           the right page. Things to be aware of are "-X", groups such as "getpwnam" to "endservent", two or
           more "=items" giving the different parameter lists, such as

               =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
               =item substr EXPR,OFFSET,LENGTH
               =item substr EXPR,OFFSET

           and different parameter lists having different meanings. (eg "select")

   compressed man pages
       Be able to install them. This would probably need a configure test to see how the system does
       compressed man pages (same directory/different directory?  same filename/different filename), as well
       as tweaking the installman script to compress as necessary.

   Add a code coverage target to the Makefile
       Make it easy for anyone to run Devel::Cover on the core's tests. The steps to do this manually are
       roughly

       •   do a normal "Configure", but include Devel::Cover as a module to install (see INSTALL for how to
           do this)

       •

               make perl

       •

               cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness

       •   Process the resulting Devel::Cover database

       This just give you the coverage of the .pms. To also get the C level coverage you need to

       •   Additionally tell "Configure" to use the appropriate C compiler flags for "gcov"

       •

               make perl.gcov

           (instead of "make perl")

       •   After running the tests run "gcov" to generate all the .gcov files.  (Including down in the
           subdirectories of ext/

       •   (From the top level perl directory) run "gcov2perl" on all the ".gcov" files to get their stats
           into the cover_db directory.

       •   Then process the Devel::Cover database

       It would be good to add a single switch to "Configure" to specify that you wanted to perform perl
       level coverage, and another to specify C level coverage, and have "Configure" and the Makefile do all
       the right things automatically.

   Make Config.pm cope with differences between built and installed perl
       Quite often vendors ship a perl binary compiled with their (pay-for) compilers.  People install a
       free compiler, such as gcc. To work out how to build extensions, Perl interrogates %Config, so in
       this situation %Config describes compilers that aren't there, and extension building fails. This
       forces people into choosing between re-compiling perl themselves using the compiler they have, or
       only using modules that the vendor ships.

       It would be good to find a way teach "Config.pm" about the installation setup, possibly involving
       probing at install time or later, so that the %Config in a binary distribution better describes the
       installed machine, when the installed machine differs from the build machine in some significant way.

   linker specification files
       Some platforms mandate that you provide a list of a shared library's external symbols to the linker,
       so the core already has the infrastructure in place to do this for generating shared perl libraries.
       My understanding is that the GNU toolchain can accept an optional linker specification file, and
       restrict visibility just to symbols declared in that file. It would be good to extend makedef.pl to
       support this format, and to provide a means within "Configure" to enable it. This would allow Unix
       users to test that the export list is correct, and to build a perl that does not pollute the global
       namespace with private symbols.

   Cross-compile support
       Currently "Configure" understands "-Dusecrosscompile" option. This option arranges for building
       "miniperl" for TARGET machine, so this "miniperl" is assumed then to be copied to TARGET machine and
       used as a replacement of full "perl" executable.

       This could be done little differently. Namely "miniperl" should be built for HOST and then full
       "perl" with extensions should be compiled for TARGET.  This, however, might require extra trickery
       for %Config: we have one config first for HOST and then another for TARGET.  Tools like MakeMaker
       will be mightily confused.  Having around two different types of executables and libraries (HOST and
       TARGET) makes life interesting for Makefiles and shell (and Perl) scripts.  There is $Config{run},
       normally empty, which can be used as an execution wrapper.  Also note that in some
       cross-compilation/execution environments the HOST and the TARGET do not see the same filesystem(s),
       the $Config{run} may need to do some file/directory copying back and forth.

   roffitall
       Make pod/roffitall be updated by pod/buildtoc.

   Split "linker" from "compiler"
       Right now, Configure probes for two commands, and sets two variables:

       •   "cc" (in cc.U)

           This variable holds the name of a command to execute a C compiler which can resolve multiple
           global references that happen to have the same name.  Usual values are cc and gcc.  Fervent ANSI
           compilers may be called c89.  AIX has xlc.

       •   "ld" (in dlsrc.U)

           This variable indicates the program to be used to link libraries for dynamic loading.  On some
           systems, it is ld.  On ELF systems, it should be $cc.  Mostly, we'll try to respect the hint file
           setting.

       There is an implicit historical assumption from around Perl5.000alpha something, that $cc is also the
       correct command for linking object files together to make an executable. This may be true on Unix,
       but it's not true on other platforms, and there are a maze of work arounds in other places (such as
       Makefile.SH) to cope with this.

       Ideally, we should create a new variable to hold the name of the executable linker program, probe for
       it in Configure, and centralise all the special case logic there or in hints files.

       A small bikeshed issue remains - what to call it, given that $ld is already taken (arguably for the
       wrong thing now, but on SunOS 4.1 it is the command for creating dynamically-loadable modules) and
       $link could be confused with the Unix command line executable of the same name, which does something
       completely different. Andy Dougherty makes the counter argument "In parrot, I tried to call the
       command used to link object files and  libraries into an executable link, since that's what my
       vaguely-remembered DOS and VMS experience suggested. I don't think any real confusion has ensued, so
       it's probably a reasonable name for perl5 to use."

       "Alas, I've always worried that introducing it would make things worse, since now the module building
       utilities would have to look for $Config{link} and institute a fall-back plan if it weren't found."
       Although I can see that as confusing, given that $Config{d_link} is true when (hard) links are
       available.

   Configure Windows using PowerShell
       Currently, Windows uses hard-coded config files based to build the config.h for compiling Perl.
       Makefiles are also hard-coded and need to be hand edited prior to building Perl. While this makes it
       easy to create a perl.exe that works across multiple Windows versions, being able to accurately
       configure a perl.exe for a specific Windows versions and VS C++ would be a nice enhancement.  With
       PowerShell available on Windows XP and up, this may now be possible.  Step 1 might be to investigate
       whether this is possible and use this to clean up our current makefile situation.  Step 2 would be to
       see if there would be a way to use our existing metaconfig units to configure a Windows Perl or
       whether we go in a separate direction and make it so.  Of course, we all know what step 3 is.

   decouple -g and -DDEBUGGING
       Currently Configure automatically adds "-DDEBUGGING" to the C compiler flags if it spots "-g" in the
       optimiser flags. The pre-processor directive "DEBUGGING" enables perl's command line "-D" options,
       but in the process makes perl slower. It would be good to disentangle this logic, so that C-level
       debugging with "-g" and Perl level debugging with "-D" can easily be enabled independently.

Tasks that need a little C knowledge
       These tasks would need a little C knowledge, but don't need any specific background or experience
       with XS, or how the Perl interpreter works

   Weed out needless PERL_UNUSED_ARG
       The C code uses the macro "PERL_UNUSED_ARG" to stop compilers warning about unused arguments. Often
       the arguments can't be removed, as there is an external constraint that determines the prototype of
       the function, so this approach is valid. However, there are some cases where "PERL_UNUSED_ARG" could
       be removed. Specifically

       •   The prototypes of (nearly all) static functions can be changed

       •   Unused arguments generated by short cut macros are wasteful - the short cut macro used can be
           changed.

   Modernize the order of directories in @INC
       The way @INC is laid out by default, one cannot upgrade core (dual-life) modules without overwriting
       files. This causes problems for binary package builders.  One possible proposal is laid out in this
       message: http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html
       <http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-04/msg02380.html>.

   -Duse32bit*
       Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.  On these systems, it might be
       the default compilation mode, and there is currently no guarantee that passing no use64bitall option
       to the Configure process will build a 32bit perl. Implementing -Duse32bit* options would be nice for
       perl 5.12.

   Profile Perl - am I hot or not?
       The Perl source code is stable enough that it makes sense to profile it, identify and optimise the
       hotspots. It would be good to measure the performance of the Perl interpreter using free tools such
       as cachegrind, gprof, and dtrace, and work to reduce the bottlenecks they reveal.

       As part of this, the idea of pp_hot.c is that it contains the hot ops, the ops that are most commonly
       used. The idea is that by grouping them, their object code will be adjacent in the executable, so
       they have a greater chance of already being in the CPU cache (or swapped in) due to being near
       another op already in use.

       Except that it's not clear if these really are the most commonly used ops. So as part of exercising
       your skills with coverage and profiling tools you might want to determine what ops really are the
       most commonly used. And in turn suggest evictions and promotions to achieve a better pp_hot.c.

       One piece of Perl code that might make a good testbed is installman.

   Allocate OPs from arenas
       Currently all new OP structures are individually malloc()ed and free()d.  All "malloc"
       implementations have space overheads, and are now as fast as custom allocates so it would both use
       less memory and less CPU to allocate the various OP structures from arenas. The SV arena code can
       probably be re-used for this.

       Note that Configuring perl with "-Accflags=-DPL_OP_SLAB_ALLOC" will use Perl_Slab_alloc() to pack
       optrees into a contiguous block, which is probably superior to the use of OP arenas, esp. from a
       cache locality standpoint.  See "Profile Perl - am I hot or not?".

   Improve win32/wince.c
       Currently, numerous functions look virtually, if not completely, identical in both "win32/wince.c"
       and "win32/win32.c" files, which can't be good.

   Use secure CRT functions when building with VC8 on Win32
       Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis that they were "unsafe"
       and introduced differently named secure versions of them as replacements, e.g. instead of writing

           FILE* f = fopen(__FILE__, "r");

       one should now write

           FILE* f;
           errno_t err = fopen_s(&f, __FILE__, "r");

       Currently, the warnings about these deprecations have been disabled by adding
       -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that warning suppressant and
       actually make use of the new secure CRT functions.

       There is also a similar issue with POSIX CRT function names like fileno having been deprecated in
       favour of ISO C++ conformant names like _fileno. These warnings are also currently suppressed by
       adding -D_CRT_NONSTDC_NO_DEPRECATE. It might be nice to do as Microsoft suggest here too, although,
       unlike the secure functions issue, there is presumably little or no benefit in this case.

   Fix POSIX::access() and chdir() on Win32
       These functions currently take no account of DACLs and therefore do not behave correctly in
       situations where access is restricted by DACLs (as opposed to the read-only attribute).

       Furthermore, POSIX::access() behaves differently for directories having the read-only attribute set
       depending on what CRT library is being used. For example, the _access() function in the VC6 and VC7
       CRTs (wrongly) claim that such directories are not writable, whereas in fact all directories are
       writable unless access is denied by DACLs. (In the case of directories, the read-only attribute
       actually only means that the directory cannot be deleted.) This CRT bug is fixed in the VC8 and VC9
       CRTs (but, of course, the directory may still not actually be writable if access is indeed denied by
       DACLs).

       For the chdir() issue, see ActiveState bug #74552: http://bugs.activestate.com/show_bug.cgi?id=74552

       Therefore, DACLs should be checked both for consistency across CRTs and for the correct answer.

       (Note that perl's -w operator should not be modified to check DACLs. It has been written so that it
       reflects the state of the read-only attribute, even for directories (whatever CRT is being used), for
       symmetry with chmod().)

   strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()
       Maybe create a utility that checks after each libperl.a creation that none of the above (nor
       sprintf(), vsprintf(), or *SHUDDER* gets()) ever creep back to libperl.a.

         nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'

       Note, of course, that this will only tell whether your platform is using those naughty interfaces.

   -D_FORTIFY_SOURCE=2, -fstack-protector
       Recent glibcs support "-D_FORTIFY_SOURCE=2" and recent gcc (4.1 onwards?) supports
       "-fstack-protector", both of which give protection against various kinds of buffer overflow problems.
       These should probably be used for compiling Perl whenever available, Configure and/or hints files
       should be adjusted to probe for the availability of these features and enable them as appropriate.

   Arenas for GPs? For MAGIC?
       "struct gp" and "struct magic" are both currently allocated by "malloc".  It might be a speed or
       memory saving to change to using arenas. Or it might not. It would need some suitable benchmarking
       first. In particular, "GP"s can probably be changed with minimal compatibility impact (probably
       nothing outside of the core, or even outside of gv.c allocates them), but they probably aren't
       allocated/deallocated often enough for a speed saving. Whereas "MAGIC" is allocated/deallocated more
       often, but in turn, is also something more externally visible, so changing the rules here may bite
       external code.

   Shared arenas
       Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and PVHV, and PVCV and
       PVFM. It should be possible to allocate and return same sized bodies from the same actual arena,
       rather than maintaining one arena for each. This could save 4-6K per thread, of memory no longer tied
       up in the not-yet-allocated part of an arena.

Tasks that need a knowledge of XS
       These tasks would need C knowledge, and roughly the level of knowledge of the perl API that comes
       from writing modules that use XS to interface to C.

   Write an XS cookbook
       Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that demonstrate common tasks
       and good practices.  (Some of these might be extracted from perlguts.) The target audience should be
       XS novices, who need more examples than perlguts but something less overwhelming than perlapi.
       Recipes should provide "one pretty good way to do it" instead of TIMTOWTDI.

       Rather than focusing on interfacing Perl to C libraries, such a cookbook should probably focus on how
       to optimize Perl routines by re-writing them in XS.  This will likely be more motivating to those who
       mostly work in Perl but are looking to take the next step into XS.

       Deconstructing and explaining some simpler XS modules could be one way to bootstrap a cookbook.
       (List::Util? Class::XSAccessor? Tree::Ternary_XS?)  Another option could be deconstructing the
       implementation of some simpler functions in op.c.

   Allow XSUBs to inline themselves as OPs
       For a simple XSUB, often the subroutine dispatch takes more time than the XSUB itself. The tokeniser
       already has the ability to inline constant subroutines - it would be good to provide a way to inline
       other subroutines.

       Specifically, simplest approach looks to be to allow an XSUB to provide an alternative implementation
       of itself as a custom OP. A new flag bit in "CvFLAGS()" would signal to the peephole optimiser to
       take an optree such as this:

           b  <@> leave[1 ref] vKP/REFC ->(end)
           1     <0> enter ->2
           2     <;> nextstate(main 1 -e:1) v:{ ->3
           a     <2> sassign vKS/2 ->b
           8        <1> entersub[t2] sKS/TARG,1 ->9
           -           <1> ex-list sK ->8
           3              <0> pushmark s ->4
           4              <$> const(IV 1) sM ->5
           6              <1> rv2av[t1] lKM/1 ->7
           5                 <$> gv(*a) s ->6
           -              <1> ex-rv2cv sK ->-7 ->7
           7                 <$> gv(*x) s/EARLYCV ->8
           -        <1> ex-rv2sv sKRM*/1 ->a
           9           <$> gvsv(*b) s ->a

       perform the symbol table lookup of "rv2cv" and "gv(*x)", locate the pointer to the custom OP that
       provides the direct implementation, and re- write the optree something like:

           b  <@> leave[1 ref] vKP/REFC ->(end)
           1     <0> enter ->2
           2     <;> nextstate(main 1 -e:1) v:{ ->3
           a     <2> sassign vKS/2 ->b
           7        <1> custom_x -> 8
           -           <1> ex-list sK ->7
           3              <0> pushmark s ->4
           4              <$> const(IV 1) sM ->5
           6              <1> rv2av[t1] lKM/1 ->7
           5                 <$> gv(*a) s ->6
           -              <1> ex-rv2cv sK ->-- ->-
           -                 <$> ex-gv(*x) s/EARLYCV ->7
           -        <1> ex-rv2sv sKRM*/1 ->a
           8           <$> gvsv(*b) s ->a

       i.e. the gv(*) OP has been nulled and spliced out of the execution path, and the "entersub" OP has
       been replaced by the custom op.

       This approach should provide a measurable speed up to simple XSUBs inside tight loops. Initially one
       would have to write the OP alternative implementation by hand, but it's likely that this should be
       reasonably straightforward for the type of XSUB that would benefit the most. Longer term, once the
       run-time implementation is proven, it should be possible to progressively update ExtUtils::ParseXS to
       generate OP implementations for some XSUBs.

   Remove the use of SVs as temporaries in dump.c
       dump.c contains debugging routines to dump out the contains of perl data structures, such as "SV"s,
       "AV"s and "HV"s. Currently, the dumping code uses "SV"s for its temporary buffers, which was a
       logical initial implementation choice, as they provide ready made memory handling.

       However, they also lead to a lot of confusion when it happens that what you're trying to debug is
       seen by the code in dump.c, correctly or incorrectly, as a temporary scalar it can use for a
       temporary buffer. It's also not possible to dump scalars before the interpreter is properly set up,
       such as during ithreads cloning. It would be good to progressively replace the use of scalars as
       string accumulation buffers with something much simpler, directly allocated by "malloc". The dump.c
       code is (or should be) only producing 7 bit US-ASCII, so output character sets are not an issue.

       Producing and proving an internal simple buffer allocation would make it easier to re-write the
       internals of the PerlIO subsystem to avoid using "SV"s for its buffers, use of which can cause
       problems similar to those of dump.c, at similar times.

   safely supporting POSIX SA_SIGINFO
       Some years ago Jarkko supplied patches to provide support for the POSIX SA_SIGINFO feature in Perl,
       passing the extra data to the Perl signal handler.

       Unfortunately, it only works with "unsafe" signals, because under safe signals, by the time Perl gets
       to run the signal handler, the extra information has been lost. Moreover, it's not easy to store it
       somewhere, as you can't call mutexs, or do anything else fancy, from inside a signal handler.

       So it strikes me that we could provide safe SA_SIGINFO support

       1.  Provide global variables for two file descriptors

       2.  When the first request is made via "sigaction" for "SA_SIGINFO", create a pipe, store the reader
           in one, the writer in the other

       3.  In the "safe" signal handler ("Perl_csighandler()"/"S_raise_signal()"), if the "siginfo_t"
           pointer non-"NULL", and the writer file handle is open,

           1.      serialise signal number, "struct siginfo_t" (or at least the parts we care about) into a
                   small auto char buff

           2.      "write()" that (non-blocking) to the writer fd

                   1.          if it writes 100%, flag the signal in a counter of "signals on the pipe" akin
                               to the current per-signal-number counts

                   2.          if it writes 0%, assume the pipe is full. Flag the data as lost?

                   3.          if it writes partially, croak a panic, as your OS is broken.

       4.  in the regular "PERL_ASYNC_CHECK()" processing, if there are "signals on the pipe", read the data
           out, deserialise, build the Perl structures on the stack (code in "Perl_sighandler()", the
           "unsafe" handler), and call as usual.

       I think that this gets us decent "SA_SIGINFO" support, without the current risk of running Perl code
       inside the signal handler context. (With all the dangers of things like "malloc" corruption that that
       currently offers us)

       For more information see the thread starting with this message:
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html

   autovivification
       Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;

       This task is incremental - even a little bit of work on it will help.

   Unicode in Filenames
       chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, opendir, qx, readdir, readlink,
       rename, rmdir, stat, symlink, sysopen, system, truncate, unlink, utime, -X.  All these could
       potentially accept Unicode filenames either as input or output (and in the case of system and qx
       Unicode in general, as input or output to/from the shell).  Whether a filesystem - an operating
       system pair understands Unicode in filenames varies.

       Known combinations that have some level of understanding include Microsoft NTFS, Apple HFS+ (In Mac
       OS 9 and X) and Apple UFS (in Mac OS X), NFS v4 is rumored to be Unicode, and of course Plan 9.  How
       to create Unicode filenames, what forms of Unicode are accepted and used (UCS-2, UTF-16, UTF-8), what
       (if any) is the normalization form used, and so on, varies.  Finding the right level of interfacing
       to Perl requires some thought.  Remember that an OS does not implicate a filesystem.

       (The Windows -C command flag "wide API support" has been at least temporarily retired in 5.8.1, and
       the -C has been repurposed, see perlrun.)

       Most probably the right way to do this would be this: "Virtualize operating system access".

   Unicode in %ENV
       Currently the %ENV entries are always byte strings.  See "Virtualize operating system access".

   Unicode and glob()
       Currently glob patterns and filenames returned from File::Glob::glob() are always byte strings.  See
       "Virtualize operating system access".

   use less 'memory'
       Investigate trade offs to switch out perl's choices on memory usage.  Particularly perl should be
       able to give memory back.

       This task is incremental - even a little bit of work on it will help.

   Re-implement ":unique" in a way that is actually thread-safe
       The old implementation made bad assumptions on several levels. A good 90% solution might be just to
       make ":unique" work to share the string buffer of SvPVs. That way large constant strings can be
       shared between ithreads, such as the configuration information in Config.

   Make tainting consistent
       Tainting would be easier to use if it didn't take documented shortcuts and allow taint to "leak"
       everywhere within an expression.

   readpipe(LIST)
       system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid running a shell. readpipe() (the
       function behind qx//) could be similarly extended.

   Audit the code for destruction ordering assumptions
       Change 25773 notes

           /* Need to check SvMAGICAL, as during global destruction it may be that
              AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
              is now part of the linked list of SV heads, rather than pointing to
              the original body.  */
           /* FIXME - audit the code for other bugs like this one.  */

       adding the "SvMAGICAL" check to

           if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
               MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);

       Go through the core and look for similar assumptions that SVs have particular types, as all bets are
       off during global destruction.

   Extend PerlIO and PerlIO::Scalar
       PerlIO::Scalar doesn't know how to truncate().  Implementing this would require extending the PerlIO
       vtable.

       Similarly the PerlIO vtable doesn't know about formats (write()), or about stat(), or
       chmod()/chown(), utime(), or flock().

       (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership would mean.)

       PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), opendir(), closedir(),
       seekdir(), rewinddir(), glob(); symlink(), readlink().

       See also "Virtualize operating system access".

   -C on the #! line
       It should be possible to make -C work correctly if found on the #! line, given that all perl command
       line options are strict ASCII, and -C changes only the interpretation of non-ASCII characters, and
       not for the script file handle. To make it work needs some investigation of the ordering of function
       calls during startup, and (by implication) a bit of tweaking of that order.

   Organize error messages
       Perl's diagnostics (error messages, see perldiag) could use reorganizing and formalizing so that each
       error message has its stable-for-all-eternity unique id, categorized by severity, type, and
       subsystem.  (The error messages would be listed in a datafile outside of the Perl source code, and
       the source code would only refer to the messages by the id.)  This clean-up and regularizing should
       apply for all croak() messages.

       This would enable all sorts of things: easier translation/localization of the messages (though please
       do keep in mind the caveats of Locale::Maketext about too straightforward approaches to translation),
       filtering by severity, and instead of grepping for a particular error message one could look for a
       stable error id.  (Of course, changing the error messages by default would break all the existing
       software depending on some particular error message...)

       This kind of functionality is known as message catalogs.  Look for inspiration for example in the
       catgets() system, possibly even use it if available-- but only if available, all platforms will not
       have catgets().

       For the really pure at heart, consider extending this item to cover also the warning messages (see
       perllexwarn, "warnings.pl").

Tasks that need a knowledge of the interpreter
       These tasks would need C knowledge, and knowledge of how the interpreter works, or a willingness to
       learn.

   forbid labels with keyword names
       Currently "goto keyword" "computes" the label value:

           $ perl -e 'goto print'
           Can't find label 1 at -e line 1.

       It is controversial if the right way to avoid the confusion is to forbid labels with keyword names,
       or if it would be better to always treat bareword expressions after a "goto" as a label and never as
       a keyword.

   truncate() prototype
       The prototype of truncate() is currently $$. It should probably be "*$" instead. (This is changed in
       opcode.pl)

   decapsulation of smart match argument
       Currently "$foo ~~ $object" will die with the message "Smart matching a non-overloaded object breaks
       encapsulation". It would be nice to allow to bypass this by using explictly the syntax "$foo ~~
       %$object" or "$foo ~~ @$object".

   error reporting of [$a ; $b]
       Using ";" inside brackets is a syntax error, and we don't propose to change that by giving it any
       meaning. However, it's not reported very helpfully:

           $ perl -e '$a = [$b; $c];'
           syntax error at -e line 1, near "$b;"
           syntax error at -e line 1, near "$c]"
           Execution of -e aborted due to compilation errors.

       It should be possible to hook into the tokeniser or the lexer, so that when a ";" is parsed where it
       is not legal as a statement terminator (ie inside "{}" used as a hashref, "[]" or "()") it issues an
       error something like ';' isn't legal inside an expression - if you need multiple statements use a do
       {...} block. See the thread starting at
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html

   lexicals used only once
       This warns:

           $ perl -we '$pie = 42'
           Name "main::pie" used only once: possible typo at -e line 1.

       This does not:

           $ perl -we 'my $pie = 42'

       Logically all lexicals used only once should warn, if the user asks for warnings.  An unworked RT
       ticket (#5087) has been open for almost seven years for this discrepancy.

   UTF-8 revamp
       The handling of Unicode is unclean in many places. For example, the regexp engine matches in Unicode
       semantics whenever the string or the pattern is flagged as UTF-8, but that should not be dependent on
       an internal storage detail of the string.

   Properly Unicode safe tokeniser and pads.
       The tokeniser isn't actually very UTF-8 clean. "use utf8;" is a hack - variable names are stored in
       stashes as raw bytes, without the utf-8 flag set. The pad API only takes a "char *" pointer, so
       that's all bytes too. The tokeniser ignores the UTF-8-ness of "PL_rsfp", or any SVs returned from
       source filters.  All this could be fixed.

   state variable initialization in list context
       Currently this is illegal:

           state ($a, $b) = foo();

       In Perl 6, "state ($a) = foo();" and "(state $a) = foo();" have different semantics, which is tricky
       to implement in Perl 5 as currently they produce the same opcode trees. The Perl 6 design is firm, so
       it would be good to implement the necessary code in Perl 5. There are comments in
       "Perl_newASSIGNOP()" that show the code paths taken by various assignment constructions involving
       state variables.

   Implement $value ~~ 0 .. $range
       It would be nice to extend the syntax of the "~~" operator to also understand numeric (and maybe
       alphanumeric) ranges.

   A does() built-in
       Like ref(), only useful. It would call the "DOES" method on objects; it would also tell whether
       something can be dereferenced as an array/hash/etc., or used as a regexp, etc.
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html
       <http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>

   Tied filehandles and write() don't mix
       There is no method on tied filehandles to allow them to be called back by formats.

   Propagate compilation hints to the debugger
       Currently a debugger started with -dE on the command-line doesn't see the features enabled by -E.
       More generally hints ($^H and "%^H") aren't propagated to the debugger. Probably it would be a good
       thing to propagate hints from the innermost non-"DB::" scope: this would make code eval'ed in the
       debugger see the features (and strictures, etc.) currently in scope.

   Attach/detach debugger from running program
       The old perltodo notes "With "gdb", you can attach the debugger to a running program if you pass the
       process ID. It would be good to do this with the Perl debugger on a running Perl program, although
       I'm not sure how it would be done." ssh and screen do this with named pipes in /tmp. Maybe we can
       too.

   LVALUE functions for lists
       The old perltodo notes that lvalue functions don't work for list or hash slices. This would be good
       to fix.

   regexp optimiser optional
       The regexp optimiser is not optional. It should configurable to be, to allow its performance to be
       measured, and its bugs to be easily demonstrated.

   "/w" regex modifier
       That flag would enable to match whole words, and also to interpolate arrays as alternations. With it,
       "/P/w" would be roughly equivalent to:

           do { local $"='|'; /\b(?:P)\b/ }

       See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html
       <http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> for the discussion.

   optional optimizer
       Make the peephole optimizer optional. Currently it performs two tasks as it walks the optree -genuine optreegenuine
       genuine peephole optimisations, and necessary fixups of ops. It would be good to find an efficient
       way to switch out the optimisations whilst keeping the fixups.

   You WANT *how* many
       Currently contexts are void, scalar and list. split has a special mechanism in place to pass in the
       number of return values wanted. It would be useful to have a general mechanism for this, backwards
       compatible and little speed hit.  This would allow proposals such as short circuiting sort to be
       implemented as a module on CPAN.

   lexical aliases
       Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".

   entersub XS vs Perl
       At the moment pp_entersub is huge, and has code to deal with entering both perl and XS subroutines.
       Subroutine implementations rarely change between perl and XS at run time, so investigate using 2 ops
       to enter subs (one for XS, one for perl) and swap between if a sub is redefined.

   Self-ties
       Self-ties are currently illegal because they caused too many segfaults. Maybe the causes of these
       could be tracked down and self-ties on all types reinstated.

   Optimize away @_
       The old perltodo notes "Look at the "reification" code in "av.c"".

   Virtualize operating system access
       Implement a set of "vtables" that virtualizes operating system access (open(), mkdir(), unlink(),
       readdir(), getenv(), etc.)  At the very least these interfaces should take SVs as "name" arguments
       instead of bare char pointers; probably the most flexible and extensible way would be for the Perl-facing Perlfacing
       facing interfaces to accept HVs.  The system needs to be per-operating-system and per-file-system
       hookable/filterable, preferably both from XS and Perl level ("Files and Filesystems" in perlport is
       good reading at this point, in fact, all of perlport is.)

       This has actually already been implemented (but only for Win32), take a look at iperlsys.h and
       win32/perlhost.h.  While all Win32 variants go through a set of "vtables" for operating system
       access, non-Win32 systems currently go straight for the POSIX/Unix-style system/library call.
       Similar system as for Win32 should be implemented for all platforms.  The existing Win32
       implementation probably does not need to survive alongside this proposed new implementation, the
       approaches could be merged.

       What would this give us?  One often-asked-for feature this would enable is using Unicode for
       filenames, and other "names" like %ENV, usernames, hostnames, and so forth.  (See "When Unicode Does
       Not Happen" in perlunicode.)

       But this kind of virtualization would also allow for things like virtual filesystems, virtual
       networks, and "sandboxes" (though as long as dynamic loading of random object code is allowed, not
       very safe sandboxes since external code of course know not of Perl's vtables).  An example of a
       smaller "sandbox" is that this feature can be used to implement per-thread working directories: Win32
       already does this.

       See also "Extend PerlIO and PerlIO::Scalar".

   Investigate PADTMP hash pessimisation
       The peephole optimiser converts constants used for hash key lookups to shared hash key scalars. Under
       ithreads, something is undoing this work.  See
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html

   Store the current pad in the OP slab allocator
       Currently we leak ops in various cases of parse failure. I suggested that we could solve this by
       always using the op slab allocator, and walking it to free ops. Dave comments that as some ops are
       already freed during optree creation one would have to mark which ops are freed, and not double free
       them when walking the slab. He notes that one problem with this is that for some ops you have to know
       which pad was current at the time of allocation, which does change. I suggested storing a pointer to
       the current pad in the memory allocated for the slab, and swapping to a new slab each time the pad
       changes. Dave thinks that this would work.

   repack the optree
       Repacking the optree after execution order is determined could allow removal of NULL ops, and optimal
       ordering of OPs with respect to cache-line filling.  The slab allocator could be reused for this
       purpose.  I think that the best way to do this is to make it an optional step just before the
       completed optree is attached to anything else, and to use the slab allocator unchanged, so that
       freeing ops is identical whether or not this step runs.  Note that the slab allocator allocates ops
       downwards in memory, so one would have to actually "allocate" the ops in reverse-execution order to
       get them contiguous in memory in execution order.

       See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html

       Note that running this copy, and then freeing all the old location ops would cause their slabs to be
       freed, which would eliminate possible memory wastage if the previous suggestion is implemented, and
       we swap slabs more frequently.

   eliminate incorrect line numbers in warnings
       This code

           use warnings;
           my $undef;

           if ($undef == 3) {
           } elsif ($undef == 0) {
           }

       used to produce this output:

           Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
           Use of uninitialized value in numeric eq (==) at wrong.pl line 4.

       where the line of the second warning was misreported - it should be line 5.  Rafael fixed this - the
       problem arose because there was no nextstate OP between the execution of the "if" and the "elsif",
       hence "PL_curcop" still reports that the currently executing line is line 4. The solution was to
       inject a nextstate OPs for each "elsif", although it turned out that the nextstate OP needed to be a
       nulled OP, rather than a live nextstate OP, else other line numbers became misreported. (Jenga!)

       The problem is more general than "elsif" (although the "elsif" case is the most common and the most
       confusing). Ideally this code

           use warnings;
           my $undef;

           my $a = $undef + 1;
           my $b
             = $undef
             + 1;

       would produce this output

           Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
           Use of uninitialized value $undef in addition (+) at wrong.pl line 7.

       (rather than lines 4 and 5), but this would seem to require every OP to carry (at least) line number
       information.

       What might work is to have an optional line number in memory just before the BASEOP structure, with a
       flag bit in the op to say whether it's present.  Initially during compile every OP would carry its
       line number. Then add a late pass to the optimiser (potentially combined with "repack the optree")
       which looks at the two ops on every edge of the graph of the execution path. If the line number
       changes, flags the destination OP with this information.  Once all paths are traced, replace every op
       with the flag with a nextstate-light op (that just updates "PL_curcop"), which in turn then passes
       control on to the true op. All ops would then be replaced by variants that do not store the line
       number. (Which, logically, why it would work best in conjunction with "repack the optree", as that is
       already copying/reallocating all the OPs)

       (Although I should note that we're not certain that doing this for the general case is worth it)

   optimize tail-calls
       Tail-calls present an opportunity for broadly applicable optimization; anywhere that "return
       foo(...)" is called, the outer return can be replaced by a goto, and foo will return directly to the
       outer caller, saving (conservatively) 25% of perl's call&return cost, which is relatively higher than
       in C.  The scheme language is known to do this heavily.  B::Concise provides good insight into where
       this optimization is possible, ie anywhere entersub,leavesub op-sequence occurs.

        perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'

       Bottom line on this is probably a new pp_tailcall function which combines the code in pp_entersub,
       pp_leavesub.  This should probably be done 1st in XS, and using B::Generate to patch the new OP into
       the optrees.

Big projects
       Tasks that will get your name mentioned in the description of the "Highlights of 5.12"

   make ithreads more robust
       Generally make ithreads more robust. See also "iCOW"

       This task is incremental - even a little bit of work on it will help, and will be greatly
       appreciated.

       One bit would be to write the missing code in sv.c:Perl_dirp_dup.

       Fix Perl_sv_dup, et al so that threads can return objects.

   iCOW
       Sarathy and Arthur have a proposal for an improved Copy On Write which specifically will be able to
       COW new ithreads. If this can be implemented it would be a good thing.

   (?{...}) closures in regexps
       Fix (or rewrite) the implementation of the "/(?{...})/" closures.

   A re-entrant regexp engine
       This will allow the use of a regex from inside (?{ }), (??{ }) and (?(?{ })|) constructs.

   Add class set operations to regexp engine
       Apparently these are quite useful. Anyway, Jeffery Friedl wants them.

       demerphq has this on his todo list, but right at the bottom.

Tasks for microperl
       [ Each and every one of these may be obsolete, but they were listed
         in the old Todo.micro file]

   make creating uconfig.sh automatic
   make creating Makefile.micro automatic
   do away with fork/exec/wait?
       (system, popen should be enough?)

   some of the uconfig.sh really needs to be probed (using cc) in buildtime:
       (uConfigure? :-) native datatype widths and endianness come to mind



perl v5.12.5                                     2012-11-03                                      PERLTODO(1)