Spec-Zone .ru
спецификации, руководства, описания, API
Spec-Zone .ru
спецификации, руководства, описания, API
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namespace(n)                                Tcl Built-In Commands                               namespace(n)



____________________________________________________________________________________________________________

NAME
       namespace - create and manipulate contexts for commands and variables

SYNOPSIS
       namespace ?subcommand? ?arg ...?
____________________________________________________________________________________________________________

DESCRIPTION
       The  namespace  command lets you create, access, and destroy separate contexts for commands and vari-ables. variables.
       ables.  See the section WHAT IS A NAMESPACE? below for a brief overview  of  namespaces.   The  legal
       values of subcommand are listed below.  Note that you can abbreviate the subcommands.

       namespace children ?namespace? ?pattern?
              Returns  a  list of all child namespaces that belong to the namespace namespace.  If namespace
              is not specified, then the children are returned for  the  current  namespace.   This  command
              returns  fully-qualified names, which start with a double colon (::).  If the optional pattern
              is given, then this command returns only the names that match  the  glob-style  pattern.   The
              actual  pattern used is determined as follows: a pattern that starts with double colon (::) is
              used directly, otherwise the namespace namespace (or the fully-qualified name of  the  current
              namespace) is prepended onto the pattern.

       namespace code script
              Captures the current namespace context for later execution of the script script.  It returns a
              new script in which script has been wrapped in a namespace inscope command.   The  new  script
              has  two  important  properties.   First,  it can be evaluated in any namespace and will cause
              script to be evaluated in the current namespace (the one where the namespace code command  was
              invoked).   Second, additional arguments can be appended to the resulting script and they will
              be passed to script as additional arguments.  For example,  suppose  the  command  set  script
              [namespace  code  {foo bar}] is invoked in namespace ::a::b.  Then eval $script [list x y] can
              be executed in any namespace (assuming the value of script has been passed  in  properly)  and
              will  have the same effect as the command ::namespace eval ::a::b {foo bar x y}.  This command
              is needed because extensions like Tk normally execute callback scripts in  the  global  names-pace. namespace.
              pace.   A  scoped command captures a command together with its namespace context in a way that
              allows it to be executed properly later.  See the section SCOPED SCRIPTS for some examples  of
              how this is used to create callback scripts.

       namespace current
              Returns  the  fully-qualified  name  for the current namespace.  The actual name of the global
              namespace is "" (i.e., an empty string), but this command returns :: for the global  namespace
              as a convenience to programmers.

       namespace delete ?namespace namespace ...?
              Each  namespace  namespace is deleted and all variables, procedures, and child namespaces con-tained contained
              tained in the namespace are deleted.  If a procedure is currently executing inside the  names-pace, namespace,
              pace,  the namespace will be kept alive until the procedure returns; however, the namespace is
              marked to prevent other code from looking it up by name.  If a namespace does not exist,  this
              command returns an error.  If no namespace names are given, this command does nothing.

       namespace ensemble subcommand ?arg ...?
              Creates  and  manipulates a command that is formed out of an ensemble of subcommands.  See the |
              section ENSEMBLES below for further details.

       namespace eval namespace arg ?arg ...?
              Activates a namespace called namespace and evaluates some code in that context.  If the names-pace namespace
              pace  does  not already exist, it is created.  If more than one arg argument is specified, the
              arguments are concatenated together with a space between each one in the same fashion  as  the
              eval command, and the result is evaluated.

              If  namespace  has  leading namespace qualifiers and any leading namespaces do not exist, they
              are automatically created.

       namespace exists namespace
              Returns 1 if namespace is a valid namespace in the current context, returns 0 otherwise.

       namespace export ?-clear? ?pattern pattern ...?
              Specifies which commands are exported from a namespace.  The exported commands are those  that
              can  be later imported into another namespace using a namespace import command.  Both commands
              defined in a namespace and commands the namespace has previously imported can be exported by a
              namespace.  The commands do not have to be defined at the time the namespace export command is
              executed.  Each pattern may contain glob-style special characters, but it may not include  any
              namespace  qualifiers.  That is, the pattern can only specify commands in the current (export-ing) (exporting)
              ing) namespace.  Each pattern is appended onto the namespace's list of  export  patterns.   If
              the  -clear  flag  is  given, the namespace's export pattern list is reset to empty before any
              pattern arguments are appended.  If no patterns are given and the -clear flag  is  not  given,
              this command returns the namespace's current export list.

       namespace forget ?pattern pattern ...?
              Removes  previously imported commands from a namespace.  Each pattern is a simple or qualified
              name such as x, foo::x or a::b::p*.  Qualified names contain double colons (::) and qualify  a
              name  with the name of one or more namespaces.  Each "qualified pattern" is qualified with the
              name of an exporting namespace and may have glob-style special characters in the command  name
              at  the  end  of the qualified name.  Glob characters may not appear in a namespace name.  For
              each "simple pattern" this command deletes the matching commands of the current namespace that
              were  imported from a different namespace.  For "qualified patterns", this command first finds
              the matching exported commands.  It then checks whether any of those commands were  previously
              imported  by  the  current  namespace.  If so, this command deletes the corresponding imported
              commands.  In effect, this un-does the action of a namespace import command.

       namespace import ?-force? ?pattern pattern ...?
              Imports commands into a namespace, or queries the set of imported  commands  in  a  namespace. |
              When  no  arguments  are present, namespace import returns the list of commands in the current |
              namespace that have been imported from other namespaces.  The commands in  the  returned  list |
              are  in the format of simple names, with no namespace qualifiers at all.  This format is suit- |
              able for composition with namespace forget (see EXAMPLES below).  When pattern  arguments  are
              present, each pattern is a qualified name like foo::x or a::p*.  That is, it includes the name
              of an exporting namespace and may have glob-style special characters in the  command  name  at
              the  end  of the qualified name.  Glob characters may not appear in a namespace name.  All the
              commands that match a pattern string and which are currently exported from their namespace are
              added  to the current namespace.  This is done by creating a new command in the current names-pace namespace
              pace that points to the exported command in its original namespace; when the new imported com-mand command
              mand is called, it invokes the exported command.  This command normally returns an error if an
              imported command conflicts with an existing command.  However, if the -force option is  given,
              imported  commands  will silently replace existing commands.  The namespace import command has
              snapshot semantics: that is, only requested commands that are currently defined in the export-ing exporting
              ing  namespace  are  imported.  In other words, you can import only the commands that are in a
              namespace at the time when the namespace import command is executed.  If  another  command  is
              defined and exported in this namespace later on, it will not be imported.

       namespace inscope namespace script ?arg ...?
              Executes  a script in the context of the specified namespace.  This command is not expected to
              be used directly by programmers; calls to it are generated implicitly  when  applications  use
              namespace  code  commands to create callback scripts that the applications then register with,
              e.g., Tk widgets.  The namespace inscope command is  much  like  the  namespace  eval  command
              except that the namespace must already exist, and namespace inscope appends additional args as
              proper list elements.

                     namespace inscope ::foo $script $x $y $z
              is equivalent to
                     namespace eval ::foo [concat $script [list $x $y $z]]
              thus additional arguments will not undergo a second round of substitution, as is the case with
              namespace eval.

       namespace origin command
              Returns the fully-qualified name of the original command to which the imported command command
              refers.  When a command is imported into a namespace, a new command is created in that  names-pace namespace
              pace  that  points to the actual command in the exporting namespace.  If a command is imported
              into a sequence of namespaces a, b,...,n where each successive namespace just imports the com-mand command
              mand  from the previous namespace, this command returns the fully-qualified name of the origi-nal original
              nal command in the first namespace, a.  If command does not refer to an imported command,  the
              command's own fully-qualified name is returned.

       namespace parent ?namespace?
              Returns  the  fully-qualified name of the parent namespace for namespace namespace.  If names-pace namespace
              pace is not specified, the fully-qualified name of the current namespace's parent is returned.

       namespace path ?namespaceList?
              Returns the command resolution path of the current namespace. If namespaceList is specified as |
              a list of named namespaces, the current namespace's command resolution path is  set  to  those |
              namespaces  and  returns  the empty list. The default command resolution path is always empty. |
              See the section NAME RESOLUTION below for an explanation of the rules regarding  name  resolu- |
              tion.

       namespace qualifiers string
              Returns any leading namespace qualifiers for string.  Qualifiers are namespace names separated
              by double colons (::).  For the string ::foo::bar::x, this command returns ::foo::bar, and for
              ::  it returns an empty string.  This command is the complement of the namespace tail command.
              Note that it does not check whether the namespace names are, in fact, the names  of  currently
              defined namespaces.

       namespace tail string
              Returns the simple name at the end of a qualified string.  Qualifiers are namespace names sep-arated separated
              arated by double colons (::).  For the string ::foo::bar::x, this command returns x,  and  for
              ::  it  returns  an  empty string.  This command is the complement of the namespace qualifiers
              command.  It does not check whether the namespace names are, in fact, the names  of  currently
              defined namespaces.

       namespace upvar namespace otherVar myVar ?otherVar myVar ...
              This  command  arranges  for  one or more local variables in the current procedure to refer to
              variables in namespace. The namespace name is resolved as described in  section  NAME  RESOLU-TION. RESOLUTION.
              TION.   The command namespace upvar $ns a b has the same behaviour as upvar 0 ${ns}::a b, with
              the sole exception of the resolution rules used for qualified  namespace  or  variable  names.
              namespace upvar returns an empty string.

       namespace unknown ?script?
              Sets or returns the unknown command handler for the current namespace.  The handler is invoked
              when a command called from within the namespace cannot be found (in either the current  names-pace namespace
              pace  or  the  global namespace).  The script argument, if given, should be a well formed list
              representing a command name and optional arguments. When the  handler  is  invoked,  the  full
              invocation  line will be appended to the script and the result evaluated in the context of the
              namespace. The default handler for all namespaces is ::unknown. If no argument  is  given,  it
              returns the handler for the current namespace.

       namespace which ?-command? ?-variable? name
              Looks up name as either a command or variable and returns its fully-qualified name.  For exam-ple, example,
              ple, if name does not exist in the current namespace but does exist in the  global  namespace,
              this  command returns a fully-qualified name in the global namespace.  If the command or vari-able variable
              able does not exist, this command returns an empty string.  If the variable has  been  created
              but  not  defined,  such as with the variable command or through a trace on the variable, this
              command will return the fully-qualified name of the variable.  If no flag is  given,  name  is
              treated  as  a  command name.  See the section NAME RESOLUTION below for an explanation of the
              rules regarding name resolution.

WHAT IS A NAMESPACE?
       A namespace is a collection of commands and variables.  It encapsulates the commands and variables to
       ensure  that  they  will  not interfere with the commands and variables of other namespaces.  Tcl has
       always had one such collection, which we refer to as the  global  namespace.   The  global  namespace
       holds  all global variables and commands.  The namespace eval command lets you create new namespaces.
       For example,
              namespace eval Counter {
                 namespace export bump
                 variable num 0

                 proc bump {} {
                    variable num
                    incr num
                 }
              }
       creates a new namespace containing the variable num and the procedure bump.  The commands  and  vari-ables variables
       ables in this namespace are separate from other commands and variables in the same program.  If there
       is a command named bump in the global namespace, for example, it will be different from  the  command
       bump in the Counter namespace.

       Namespace  variables  resemble  global  variables  in Tcl.  They exist outside of the procedures in a
       namespace but can be accessed in a procedure via the variable command, as shown in the example above.

       Namespaces  are dynamic.  You can add and delete commands and variables at any time, so you can build
       up the contents of a namespace over time using a series of namespace eval commands.  For example, the
       following series of commands has the same effect as the namespace definition shown above:
              namespace eval Counter {
                 variable num 0
                 proc bump {} {
                    variable num
                    return [incr num]
                 }
              }
              namespace eval Counter {
                 proc test {args} {
                    return $args
                 }
              }
              namespace eval Counter {
                  rename test ""
              }
       Note that the test procedure is added to the Counter namespace, and later removed via the rename com-mand. command.
       mand.

       Namespaces can have other namespaces within them, so they nest hierarchically.  A nested namespace is
       encapsulated inside its parent namespace and can not interfere with other namespaces.

QUALIFIED NAMES
       Each  namespace  has  a  textual  name such as history or ::safe::interp.  Since namespaces may nest,
       qualified names are used to refer to commands,  variables,  and  child  namespaces  contained  inside
       namespaces.  Qualified names are similar to the hierarchical path names for Unix files or Tk widgets,
       except that :: is used as the separator instead of / or ..  The topmost or global namespace  has  the
       name   ""   (i.e.,   an  empty  string),  although  ::  is  a  synonym.   As  an  example,  the  name
       ::safe::interp::create refers to the command create in the namespace interp that is a child of names-pace namespace
       pace ::safe, which in turn is a child of the global namespace, ::.

       If  you want to access commands and variables from another namespace, you must use some extra syntax.
       Names must be qualified by the namespace that contains them.  From the  global  namespace,  we  might
       access the Counter procedures like this:
              Counter::bump 5
              Counter::Reset
       We could access the current count like this:
              puts "count = $Counter::num"
       When  one namespace contains another, you may need more than one qualifier to reach its elements.  If
       we had a namespace Foo that contained the namespace Counter, you could invoke its bump procedure from
       the global namespace like this:
              Foo::Counter::bump 3

       You  can  also use qualified names when you create and rename commands.  For example, you could add a
       procedure to the Foo namespace like this:
              proc Foo::Test {args} {return $args}
       And you could move the same procedure to another namespace like this:
              rename Foo::Test Bar::Test

       There are a few remaining points about  qualified  names  that  we  should  cover.   Namespaces  have
       nonempty  names  except  for the global namespace.  :: is disallowed in simple command, variable, and
       namespace names except as a namespace separator.  Extra colons in any separator part of  a  qualified
       name  are  ignored; i.e. two or more colons are treated as a namespace separator.  A trailing :: in a
       qualified variable or command name refers to the variable or command named {}.  However,  a  trailing
       :: in a qualified namespace name is ignored.

NAME RESOLUTION
       In  general,  all  Tcl  commands  that take variable and command names support qualified names.  This
       means you can give qualified names to such commands as set, proc, rename, and interp alias.   If  you
       provide  a fully-qualified name that starts with a ::, there is no question about what command, vari-able, variable,
       able, or namespace you mean.  However, if the name does not start with a :: (i.e., is relative),  Tcl
       follows  basic  rules  for  looking it up: Variable names are always resolved by looking first in the
       current namespace, and then in the global namespace.  Command names are also always resolved by look- |
       ing  in  the current namespace first. If not found there, they are searched for in every namespace on |
       the current namespace's command path (which is empty by default). If not found there,  command  names |
       are  looked  up  in  the  global  namespace (or, failing that, are processed by the unknown command.)
       Namespace names, on the other hand, are always resolved by looking in only the current namespace.

       In the following example,
              set traceLevel 0
              namespace eval Debug {
                 printTrace $traceLevel
              }
       Tcl looks for traceLevel in the namespace Debug and then in the global namespace.  It  looks  up  the
       command  printTrace  in  the same way.  If a variable or command name is not found in either context,
       the name is undefined.  To make this point absolutely clear, consider the following example:
              set traceLevel 0
              namespace eval Foo {
                 variable traceLevel 3

                 namespace eval Debug {
                    printTrace $traceLevel
                 }
              }
       Here Tcl looks for traceLevel first in the namespace Foo::Debug.  Since it is not  found  there,  Tcl
       then looks for it in the global namespace.  The variable Foo::traceLevel is completely ignored during
       the name resolution process.

       You can use the namespace which command to clear up any question about name resolution.  For example,
       the command:
              namespace eval Foo::Debug {namespace which -variable traceLevel}
       returns ::traceLevel.  On the other hand, the command,
              namespace eval Foo {namespace which -variable traceLevel}
       returns ::Foo::traceLevel.

       As  mentioned  above,  namespace names are looked up differently than the names of variables and com-mands. commands.
       mands.  Namespace names are always resolved in the current namespace.  This means, for example,  that
       a namespace eval command that creates a new namespace always creates a child of the current namespace
       unless the new namespace name begins with ::.

       Tcl has no access control to limit what variables, commands, or namespaces you can reference.  If you
       provide  a  qualified  name  that  resolves  to an element by the name resolution rule above, you can
       access the element.

       You can access a namespace variable from a procedure in the same namespace by using the variable com-mand. command.
       mand.   Much like the global command, this creates a local link to the namespace variable.  If neces-sary, necessary,
       sary, it also creates the variable in the current namespace and initializes it.  Note that the global
       command  only creates links to variables in the global namespace.  It is not necessary to use a vari-able variable
       able command if you always refer to the namespace variable using an appropriate qualified name.

IMPORTING COMMANDS
       Namespaces are often used to represent libraries.  Some library commands are used so frequently  that
       it  is  a nuisance to type their qualified names.  For example, suppose that all of the commands in a
       package like BLT are contained in a namespace called Blt.  Then you might access these commands  like
       this:
              Blt::graph .g -background red
              Blt::table . .g 0,0
       If  you  use  the  graph and table commands frequently, you may want to access them without the Blt::
       prefix.  You can do this by importing the commands into the current namespace, like this:
              namespace import Blt::*
       This adds all exported commands from the Blt namespace into the current namespace context, so you can
       write code like this:
              graph .g -background red
              table . .g 0,0
       The namespace import command only imports commands from a namespace that that namespace exported with
       a namespace export command.

       Importing every command from a namespace is generally a bad idea since you do not know what you  will
       get.  It is better to import just the specific commands you need.  For example, the command
              namespace import Blt::graph Blt::table
       imports only the graph and table commands into the current context.

       If  you  try  to import a command that already exists, you will get an error.  This prevents you from
       importing the same command from two different packages.  But from time to time (perhaps  when  debug-ging), debugging),
       ging),  you  may  want  to get around this restriction.  You may want to reissue the namespace import
       command to pick up new commands that have appeared in a namespace.  In that case,  you  can  use  the
       -force option, and existing commands will be silently overwritten:
              namespace import -force Blt::graph Blt::table
       If  for  some reason, you want to stop using the imported commands, you can remove them with a names-pace namespace
       pace forget command, like this:
              namespace forget Blt::*
       This searches the current namespace for any commands imported from Blt.  If it finds any, it  removes
       them.  Otherwise, it does nothing.  After this, the Blt commands must be accessed with the Blt:: pre-fix. prefix.
       fix.

       When you delete a command from the exporting namespace like this:
              rename Blt::graph ""
       the command is automatically removed from all namespaces that import it.

EXPORTING COMMANDS
       You can export commands from a namespace like this:
              namespace eval Counter {
                 namespace export bump reset
                 variable Num 0
                 variable Max 100

                 proc bump {{by 1}} {
                    variable Num
                    incr Num $by
                    Check
                    return $Num
                 }
                 proc reset {} {
                    variable Num
                    set Num 0
                 }
                 proc Check {} {
                    variable Num
                    variable Max
                    if {$Num > $Max} {
                       error "too high!"
                    }
                 }
              }
       The procedures bump and reset are exported, so they are included when you  import  from  the  Counter
       namespace, like this:
              namespace import Counter::*
       However, the Check procedure is not exported, so it is ignored by the import operation.

       The namespace import command only imports commands that were declared as exported by their namespace.
       The namespace export command specifies what commands may be  imported  by  other  namespaces.   If  a
       namespace import command specifies a command that is not exported, the command is not imported.

SCOPED SCRIPTS
       The  namespace code command is the means by which a script may be packaged for evaluation in a names-pace namespace
       pace other than the one in which it was created.  It is used most often to create event handlers,  Tk
       bindings,  and  traces  for evaluation in the global context.  For instance, the following code indi-cates indicates
       cates how to direct a variable trace callback into the current namespace:

              namespace eval a {
                 variable b
                 proc theTraceCallback { n1 n2 op } {
                    upvar 1 $n1 var
                    puts "the value of $n1 has changed to $var"
                    return
                 }
                 trace add variable b write [namespace code theTraceCallback]
              }
              set a::b c

       When executed, it prints the message:

              the value of a::b has changed to c

ENSEMBLES
       The namespace ensemble is used to create and manipulate ensemble commands, which are commands  formed |
       by  grouping  subcommands  together.  The commands typically come from the current namespace when the |
       ensemble was created, though this is configurable.  Note that there may be any  number  of  ensembles |
       associated  with  any  namespace (including none, which is true of all namespaces by default), though |
       all the ensembles associated with a namespace are deleted when that namespace is deleted.   The  link |
       between an ensemble command and its namespace is maintained however the ensemble is renamed.          |

       Three subcommands of the namespace ensemble command are defined:                                      |

       namespace ensemble create ?option value                                                               |
       ...?                                                          |                                       |
              Creates a new ensemble command linked to the current namespace, returning the fully  qualified |
              name  of the command created.  The arguments to namespace ensemble create allow the configura- |
              tion of the command as if with the namespace ensemble configure command.   If  not  overridden |
              with  the  -command option, this command creates an ensemble with exactly the same name as the |
              linked namespace.  See the section ENSEMBLE OPTIONS below for a full list of options supported |
              and their effects.                                                                             |

       namespace ensemble configure command ?option? ?value                                                  |
       ...?                                             |                                                    |
              Retrieves the value of an option associated  with  the  ensemble  command  named  command,  or |
              updates  some options associated with that ensemble command.  See the section ENSEMBLE OPTIONS |
              below for a full list of options supported and their effects.                                  |

       namespace ensemble exists com-                                                                        |
       mand                                                                     |                            |
              Returns  a  boolean value that describes whether the command command exists and is an ensemble |
              command.  This command only ever returns an error if the number of arguments to the command is |
              wrong.                                                                                         |

       When  called,  an  ensemble  command takes its first argument and looks it up (according to the rules |
       described below) to discover a list of words to replace the ensemble  command  and  subcommand  with. |
       The resulting list of words is then evaluated (with no further substitutions) as if that was what was |
       typed originally (i.e. by passing the list of words through Tcl_EvalObjv) and returning the result of |
       the command.  Note that it is legal to make the target of an ensemble rewrite be another (or even the |
       same) ensemble command.  The ensemble command will not be visible through the use of the  uplevel  or |
       info level commands.                                                                                  |

   ENSEMBLE OPTIONS                                                                                          |
       The  following  options,  supported by the namespace ensemble create and namespace ensemble configure |
       commands, control how an ensemble command behaves:                                                    |

       -map                                                                                                  ||
              When  non-empty,  this  option  supplies  a dictionary that provides a mapping from subcommand |
              names to a list of prefix words to substitute in place of the ensemble command and  subcommand |
              words  (in  a manner similar to an alias created with interp alias; the words are not reparsed |
              after substitution).  When this option is empty, the mapping will be from the  local  name  of |
              the  subcommand  to its fully-qualified name.  Note that when this option is non-empty and the |
              -subcommands option is empty, the ensemble subcommand names will be exactly those  words  that |
              have mappings in the dictionary.                                                               |

       -pre-                                                                                                 |
       fixes                                                                                             |   |
              This option (which is enabled by default) controls whether  the  ensemble  command  recognizes |
              unambiguous prefixes of its subcommands.  When turned off, the ensemble command requires exact |
              matching of subcommand names.                                                                  |

       -subcom-                                                                                              |
       mands                                                                                          |      |
              When  non-empty,  this option lists exactly what subcommands are in the ensemble.  The mapping |
              for each of those commands will be either whatever is defined in the -map option,  or  to  the |
              command  with the same name in the namespace linked to the ensemble.  If this option is empty, |
              the subcommands of the namespace will either be the keys of the dictionary listed in the  -map |
              option  or  the exported commands of the linked namespace at the time of the invocation of the |
              ensemble command.                                                                              |

       -unknown                                                                                              ||
              When  non-empty, this option provides a partial command (to which all the words that are argu- |
              ments to the ensemble command,  including  the  fully-qualified  name  of  the  ensemble,  are |
              appended)  to  handle the case where an ensemble subcommand is not recognized and would other- |
              wise generate an error.  When empty (the default) an error (in the style  of  Tcl_GetIndexFro- |
              mObj)  is generated whenever the ensemble is unable to determine how to implement a particular |
              subcommand.  See UNKNOWN HANDLER BEHAVIOUR for more details.                                   |

       The following extra option is allowed by namespace ensemble create:                                   |

       -com-                                                                                                 |
       mand                                                                                              |   |
              This write-only option allows the name of the ensemble created by namespace ensemble create to |
              be anything in any existing namespace.  The default value for this option is the  fully-quali- |
              fied name of the namespace in which the namespace ensemble create command is invoked.          |

       The following extra option is allowed by namespace ensemble configure:                                |

       -names-                                                                                               |
       pace                                                                                            |     |
              This read-only option allows the retrieval of the fully-qualified name of the namespace  which |
              the ensemble was created within.                                                               |

   UNKNOWN HANDLER BEHAVIOUR                                                                                 |
       If  an unknown handler is specified for an ensemble, that handler is called when the ensemble command |
       would otherwise return an error due to it being unable to decide  which  subcommand  to  invoke.  The |
       exact  conditions  under  which  that  occurs  are controlled by the -subcommands, -map and -prefixes |
       options as described above.                                                                           |

       To execute the unknown handler, the ensemble  mechanism  takes  the  specified  -unknown  option  and |
       appends  each  argument  of the attempted ensemble command invocation (including the ensemble command |
       itself, expressed as a fully qualified name). It invokes the resulting command in the  scope  of  the |
       attempted  call.  If  the  execution  of the unknown handler terminates normally, the ensemble engine |
       reparses the subcommand (as described below) and tries to dispatch it again, which is ideal for  when |
       the  ensemble's  configuration  has been updated by the unknown subcommand handler. Any other kind of |
       termination of the unknown handler is treated as an error.                                            |

       The result of the unknown handler is expected to be a list (it is an error if it is not). If the list |
       is  an  empty list, the ensemble command attempts to look up the original subcommand again and, if it |
       is not found this time, an error will be generated just as if the  -unknown  handler  was  not  there |
       (i.e. for any particular invocation of an ensemble, its unknown handler will be called at most once.) |
       This makes it easy for the unknown handler to update the ensemble or its backing namespace so  as  to |
       provide an implementation of the desired subcommand and reparse.                                      |

       When  the result is a non-empty list, the words of that list are used to replace the ensemble command |
       and subcommand, just as if they had been looked up in the -map. It is up to the  unknown  handler  to |
       supply  all namespace qualifiers if the implementing subcommand is not in the namespace of the caller |
       of the ensemble command. Also note that when ensemble commands are chained (e.g. if you make  one  of |
       the  commands that implement an ensemble subcommand into an ensemble, in a manner similar to the text |
       widget's tag and mark subcommands) then the rewrite happens in the context of the caller of the  out- |
       ermost  ensemble.  That is to say that ensembles do not in themselves place any namespace contexts on |
       the Tcl call stack.                                                                                   |

       Where an empty -unknown handler is given (the default), the ensemble command will generate  an  error |
       message based on the list of commands that the ensemble has defined (formatted similarly to the error |
       message from Tcl_GetIndexFromObj). This is the error that will be thrown when the subcommand is still |
       not recognized during reparsing. It is also an error for an -unknown handler to delete its namespace.

EXAMPLES
       Create a namespace containing a variable and an exported command:
              namespace eval foo {
                 variable bar 0
                 proc grill {} {
                    variable bar
                    puts "called [incr bar] times"
                 }
                 namespace export grill
              }

       Call the command defined in the previous example in various ways.
              # Direct call
              ::foo::grill

              # Use the command resolution path to find the name
              namespace eval boo {
                 namespace path ::foo
                 grill
              }

              # Import into current namespace, then call local alias
              namespace import foo::grill
              grill

              # Create two ensembles, one with the default name and one with a
              # specified name.  Then call through the ensembles.
              namespace eval foo {
                 namespace ensemble create
                 namespace ensemble create -command ::foobar
              }
              foo grill
              foobar grill

       Look up where the command imported in the previous example came from:
              puts "grill came from [namespace origin grill]"

       Remove all imported commands from the current namespace:
              namespace forget {*}[namespace import]

SEE ALSO
       interp(n), upvar(n), variable(n)

KEYWORDS
       command, ensemble, exported, internal, variable



Tcl                                                  8.5                                        namespace(n)

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