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Params::Classify(3)                  User Contributed Perl Documentation                 Params::Classify(3)



NAME
       Params::Classify - argument type classification

SYNOPSIS
               use Params::Classify qw(
                       scalar_class
                       is_undef check_undef
                       is_string check_string
                       is_number check_number
                       is_glob check_glob
                       is_regexp check_regexp
                       is_ref check_ref ref_type
                       is_blessed check_blessed blessed_class
                       is_strictly_blessed check_strictly_blessed
                       is_able check_able
               );

               $c = scalar_class($arg);

               if(is_undef($arg)) {
               check_undef($arg);

               if(is_string($arg)) {
               check_string($arg);
               if(is_number($arg)) {
               check_number($arg);

               if(is_glob($arg)) {
               check_glob($arg);
               if(is_regexp($arg)) {
               check_regexp($arg);

               if(is_ref($arg)) {
               check_ref($arg);
               $t = ref_type($arg);
               if(is_ref($arg, "HASH")) {
               check_ref($arg, "HASH");

               if(is_blessed($arg)) {
               check_blessed($arg);
               if(is_blessed($arg, "IO::Handle")) {
               check_blessed($arg, "IO::Handle");
               $c = blessed_class($arg);
               if(is_strictly_blessed($arg, "IO::Pipe::End")) {
               check_strictly_blessed($arg, "IO::Pipe::End");
               if(is_able($arg, ["print", "flush"])) {
               check_able($arg, ["print", "flush"]);

DESCRIPTION
       This module provides various type-testing functions.  These are intended for functions that, unlike
       most Perl code, care what type of data they are operating on.  For example, some functions wish to
       behave differently depending on the type of their arguments (like overloaded functions in C++).

       There are two flavours of function in this module.  Functions of the first flavour only provide type
       classification, to allow code to discriminate between argument types.  Functions of the second
       flavour package up the most common type of type discrimination: checking that an argument is of an
       expected type.  The functions come in matched pairs, of the two flavours, and so the type enforcement
       functions handle only the simplest requirements for arguments of the types handled by the
       classification functions.  Enforcement of more complex types may, of course, be built using the
       classification functions, or it may be more convenient to use a module designed for the more complex
       job, such as Params::Validate.

       This module is implemented in XS, with a pure Perl backup version for systems that can't handle XS.

TYPE CLASSIFICATION
       This module divides up scalar values into the following classes:

       •   undef

       •   string (defined ordinary scalar)

       •   typeglob (yes, typeglobs fit into scalar variables)

       •   regexp (first-class regular expression objects in Perl 5.11 onwards)

       •   reference to unblessed object (further classified by physical data type of the referenced object)

       •   reference to blessed object (further classified by class blessed into)

       These classes are mutually exclusive and should be exhaustive.  This classification has been chosen
       as the most useful when one wishes to discriminate between types of scalar.  Other classifications
       are possible.  (For example, the two reference classes are distinguished by a feature of the
       referenced object; Perl does not internally treat this as a feature of the reference.)

FUNCTIONS
       Each of these functions takes one scalar argument (ARG) to be tested, possibly with other arguments
       specifying details of the test.  Any scalar value is acceptable for the argument to be tested.  Each
       "is_" function returns a simple truth value result, which is true iff ARG is of the type being
       checked for.  Each "check_" function will return normally if the argument is of the type being
       checked for, or will "die" if it is not.

   Classification
       scalar_class(ARG)
           Determines which of the five classes described above ARG falls into.  Returns "UNDEF", "STRING",
           "GLOB", "REGEXP", "REF", or "BLESSED" accordingly.

   The Undefined Value
       is_undef(ARG)
       check_undef(ARG)
           Check whether ARG is "undef".  "is_undef(ARG)" is precisely equivalent to "!defined(ARG)", and is
           included for completeness.

   Strings
       is_string(ARG)
       check_string(ARG)
           Check whether ARG is defined and is an ordinary scalar value (not a reference, typeglob, or
           regexp).  This is what one usually thinks of as a string in Perl.  In fact, any scalar (including
           "undef" and references) can be coerced to a string, but if you're trying to classify a scalar
           then you don't want to do that.

       is_number(ARG)
       check_number(ARG)
           Check whether ARG is defined and an ordinary scalar (i.e., satisfies "is_string" above) and is an
           acceptable number to Perl.  This is what one usually thinks of as a number.

           Note that simple ("is_string"-satisfying) scalars may have independent numeric and string values,
           despite the usual pretence that they have only one value.  Such a scalar is deemed to be a number
           if either it already has a numeric value (e.g., was generated by a numeric literal or an
           arithmetic computation) or its string value has acceptable syntax for a number (so it can be
           converted).  Where a scalar has separate numeric and string values (see "dualvar" in
           Scalar::Util), it is possible for it to have an acceptable numeric value while its string value
           does not have acceptable numeric syntax.  Be careful to use such a value only in a numeric
           context, if you are using it as a number.  "scalar_num_part" in Scalar::Number extracts the
           numeric part of a scalar as an ordinary number.  ("0+ARG" suffices for that unless you need to
           preserve floating point signed zeroes.)

           A number may be either a native integer or a native floating point value, and there are several
           subtypes of floating point value.  For classification, and other handling of numbers in scalars,
           see Scalar::Number.  For details of the two numeric data types, see Data::Integer and
           Data::Float.

           This function differs from "looks_like_number" (see "looks_like_number" in Scalar::Util; also
           "looks_like_number" in perlapi for a lower-level description) in excluding "undef", typeglobs,
           and references.  Why "looks_like_number" returns true for "undef" or typeglobs is anybody's
           guess.  References, if treated as numbers, evaluate to the address in memory that they reference;
           this is useful for comparing references for equality, but it is not otherwise useful to treat
           references as numbers.  Blessed references may have overloaded numeric operators, but if so then
           they don't necessarily behave like ordinary numbers.  "looks_like_number" is also confused by
           dualvars: it looks at the string portion of the scalar.

   Typeglobs
       is_glob(ARG)
       check_glob(ARG)
           Check whether ARG is a typeglob.

   Regexps
       is_regexp(ARG)
       check_regexp(ARG)
           Check whether ARG is a regexp object.

   References to Unblessed Objects
       is_ref(ARG)
       check_ref(ARG)
           Check whether ARG is a reference to an unblessed object.  If it is, then the referenced data type
           can be determined using "ref_type" (see below), which will return a string such as "HASH" or
           "SCALAR".

       ref_type(ARG)
           Returns "undef" if ARG is not a reference to an unblessed object.  Otherwise, determines what
           type of object is referenced.  Returns "SCALAR", "ARRAY", "HASH", "CODE", "FORMAT", or "IO"
           accordingly.

           Note that, unlike "ref", this does not distinguish between different types of referenced scalar.
           A reference to a string and a reference to a reference will both return "SCALAR".  Consequently,
           what "ref_type" returns for a particular reference will not change due to changes in the value of
           the referent, except for the referent being blessed.

       is_ref(ARG, TYPE)
       check_ref(ARG, TYPE)
           Check whether ARG is a reference to an unblessed object of type TYPE, as determined by
           "ref_type".  TYPE must be a string.  Possible TYPEs are "SCALAR", "ARRAY", "HASH", "CODE",
           "FORMAT", and "IO".

   References to Blessed Objects
       is_blessed(ARG)
       check_blessed(ARG)
           Check whether ARG is a reference to a blessed object.  If it is, then the class into which the
           object was blessed can be determined using "blessed_class".

       is_blessed(ARG, CLASS)
       check_blessed(ARG, CLASS)
           Check whether ARG is a reference to a blessed object that claims to be an instance of CLASS (via
           its "isa" method; see "isa" in perlobj).  CLASS must be a string, naming a Perl class.

       blessed_class(ARG)
           Returns "undef" if ARG is not a reference to a blessed object.  Otherwise, returns the class into
           which the object is blessed.

           "ref" (see "ref" in perlfunc) gives the same result on references to blessed objects, but
           different results on other types of value.  "blessed_class" is actually identical to "blessed" in
           Scalar::Util.

       is_strictly_blessed(ARG)
       check_strictly_blessed(ARG)
           Check whether ARG is a reference to a blessed object, identically to "is_blessed".  This exists
           only for symmetry; the useful form of "is_strictly_blessed" appears below.

       is_strictly_blessed(ARG, CLASS)
       check_strictly_blessed(ARG, CLASS)
           Check whether ARG is a reference to an object blessed into CLASS exactly.  CLASS must be a
           string, naming a Perl class.  Because this excludes subclasses, this is rarely what one wants,
           but there are some specialised occasions where it is useful.

       is_able(ARG)
       check_able(ARG)
           Check whether ARG is a reference to a blessed object, identically to "is_blessed".  This exists
           only for symmetry; the useful form of "is_able" appears below.

       is_able(ARG, METHODS)
       check_able(ARG, METHODS)
           Check whether ARG is a reference to a blessed object that claims to implement the methods
           specified by METHODS (via its "can" method; see "can" in perlobj).  METHODS must be either a
           single method name or a reference to an array of method names.  Each method name is a string.
           This interface check is often more appropriate than a direct ancestry check (such as "is_blessed"
           performs).

BUGS
       Probably ought to handle something like Params::Validate's scalar type specification system, which
       makes much the same distinctions.

SEE ALSO
       Data::Float, Data::Integer, Params::Validate, Scalar::Number, Scalar::Util

AUTHOR
       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT
       Copyright (C) 2004, 2006, 2007, 2009, 2010 Andrew Main (Zefram) <zefram@fysh.org>

       Copyright (C) 2009, 2010 PhotoBox Ltd

LICENSE
       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.



perl v5.16.2                                     2013-08-25                              Params::Classify(3)