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Exporter ()
  • >> Exporter (3) ( Solaris man: Библиотечные вызовы )
  • Exporter (3) ( Разные man: Библиотечные вызовы )
  • 
    
    

    NAME

         Exporter - Implements default import method for modules
    
    
    

    SYNOPSIS

         In module ModuleName.pm:
    
           package ModuleName;
           require Exporter;
           @ISA = qw(Exporter);
    
           @EXPORT = qw(...);            # symbols to export by default
           @EXPORT_OK = qw(...);         # symbols to export on request
           %EXPORT_TAGS = tag => [...];  # define names for sets of symbols
    
         In other files which wish to use ModuleName:
    
           use ModuleName;               # import default symbols into my package
    
           use ModuleName qw(...);       # import listed symbols into my package
    
           use ModuleName ();            # do not import any symbols
    
    
    
    

    DESCRIPTION

         The Exporter module implements a default `import' method
         which many modules choose to inherit rather than implement
         their own.
    
         Perl automatically calls the `import' method when processing
         a `use' statement for a module. Modules and `use' are
         documented in the perlfunc manpage and the perlmod manpage.
         Understanding the concept of modules and how the `use'
         statement operates is important to understanding the
         Exporter.
    
         How to Export
    
         The arrays `@EXPORT' and `@EXPORT_OK' in a module hold lists
         of symbols that are going to be exported into the users name
         space by default, or which they can request to be exported,
         respectively.  The symbols can represent functions, scalars,
         arrays, hashes, or typeglobs.  The symbols must be given by
         full name with the exception that the ampersand in front of
         a function is optional, e.g.
    
             @EXPORT    = qw(afunc $scalar @array);   # afunc is a function
             @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
    
    
    
         Selecting What To Export
    
         Do not export method names!
    
         Do not export anything else by default without a good
         reason!
    
         Exports pollute the namespace of the module user.  If you
         must export try to use @EXPORT_OK in preference to @EXPORT
         and avoid short or common symbol names to reduce the risk of
         name clashes.
    
         Generally anything not exported is still accessible from
         outside the module using the ModuleName::item_name (or
         $blessed_ref->method) syntax.  By convention you can use a
         leading underscore on names to informally indicate that they
         are 'internal' and not for public use.
    
         (It is actually possible to get private functions by saying:
    
           my $subref = sub { ... };
           &$subref;
    
         But there's no way to call that directly as a method, since
         a method must have a name in the symbol table.)
    
         As a general rule, if the module is trying to be object
         oriented then export nothing. If it's just a collection of
         functions then @EXPORT_OK anything but use @EXPORT with
         caution.
    
         Other module design guidelines can be found in the perlmod
         manpage.
    
         Specialised Import Lists
    
         If the first entry in an import list begins with !, : or /
         then the list is treated as a series of specifications which
         either add to or delete from the list of names to import.
         They are processed left to right. Specifications are in the
         form:
    
             [!]name         This name only
             [!]:DEFAULT     All names in @EXPORT
             [!]:tag         All names in $EXPORT_TAGS{tag} anonymous list
             [!]/pattern/    All names in @EXPORT and @EXPORT_OK which match
    
         A leading ! indicates that matching names should be deleted
         from the list of names to import.  If the first
         specification is a deletion it is treated as though preceded
         by :DEFAULT. If you just want to import extra names in
         addition to the default set you will still need to include
         :DEFAULT explicitly.
    
         e.g., Module.pm defines:
    
             @EXPORT      = qw(A1 A2 A3 A4 A5);
             @EXPORT_OK   = qw(B1 B2 B3 B4 B5);
             %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
    
             Note that you cannot use tags in @EXPORT or @EXPORT_OK.
             Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
    
         An application using Module can say something like:
    
             use Module qw(:DEFAULT :T2 !B3 A3);
    
         Other examples include:
    
             use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
             use POSIX  qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
    
         Remember that most patterns (using //) will need to be
         anchored with a leading ^, e.g., `/^EXIT/' rather than
         `/EXIT/'.
    
         You can say `BEGIN { $Exporter::Verbose=1 }' to see how the
         specifications are being processed and what is actually
         being imported into modules.
    
         Exporting without using Export's import method
    
         Exporter has a special method, 'export_to_level' which is
         used in situations where you can't directly call Export's
         import method. The export_to_level method looks like:
    
         MyPackage->export_to_level($where_to_export, $package,
         @what_to_export);
    
         where $where_to_export is an integer telling how far up the
         calling stack to export your symbols, and @what_to_export is
         an array telling what symbols *to* export (usually this is
         @_).  The $package argument is currently unused.
    
         For example, suppose that you have a module, A, which
         already has an import function:
    
         package A;
    
         @ISA = qw(Exporter); @EXPORT_OK = qw ($b);
    
         sub import {
             $A::b = 1;     # not a very useful import method }
    
         and you want to Export symbol $A::b back to the module that
         called package A. Since Exporter relies on the import method
         to work, via inheritance, as it stands Exporter::import()
         will never get called. Instead, say the following:
    
         package A; @ISA = qw(Exporter); @EXPORT_OK = qw ($b);
    
         sub import {
             $A::b = 1;
             A->export_to_level(1, @_); }
    
         This will export the symbols one level 'above' the current
         package - ie: to the program or module that used package A.
    
         Note: Be careful not to modify '@_' at all before you call
         export_to_level - or people using your package will get very
         unexplained results!
    
         Module Version Checking
    
         The Exporter module will convert an attempt to import a
         number from a module into a call to $module_name-
         >require_version($value). This can be used to validate that
         the version of the module being used is greater than or
         equal to the required version.
    
         The Exporter module supplies a default require_version
         method which checks the value of $VERSION in the exporting
         module.
    
         Since the default require_version method treats the $VERSION
         number as a simple numeric value it will regard version 1.10
         as lower than 1.9. For this reason it is strongly
         recommended that you use numbers with at least two decimal
         places, e.g., 1.09.
    
         Managing Unknown Symbols
    
         In some situations you may want to prevent certain symbols
         from being exported. Typically this applies to extensions
         which have functions or constants that may not exist on some
         systems.
    
         The names of any symbols that cannot be exported should be
         listed in the `@EXPORT_FAIL' array.
    
         If a module attempts to import any of these symbols the
         Exporter will give the module an opportunity to handle the
         situation before generating an error. The Exporter will call
         an export_fail method with a list of the failed symbols:
    
    
           @failed_symbols = $module_name->export_fail(@failed_symbols);
    
         If the export_fail method returns an empty list then no
         error is recorded and all the requested symbols are
         exported. If the returned list is not empty then an error is
         generated for each symbol and the export fails. The Exporter
         provides a default export_fail method which simply returns
         the list unchanged.
    
         Uses for the export_fail method include giving better error
         messages for some symbols and performing lazy architectural
         checks (put more symbols into @EXPORT_FAIL by default and
         then take them out if someone actually tries to use them and
         an expensive check shows that they are usable on that
         platform).
    
         Tag Handling Utility Functions
    
         Since the symbols listed within %EXPORT_TAGS must also
         appear in either @EXPORT or @EXPORT_OK, two utility
         functions are provided which allow you to easily add tagged
         sets of symbols to @EXPORT or @EXPORT_OK:
    
           %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
    
           Exporter::export_tags('foo');     # add aa, bb and cc to @EXPORT
           Exporter::export_ok_tags('bar');  # add aa, cc and dd to @EXPORT_OK
    
         Any names which are not tags are added to @EXPORT or
         @EXPORT_OK unchanged but will trigger a warning (with `-w')
         to avoid misspelt tags names being silently added to @EXPORT
         or @EXPORT_OK. Future versions may make this a fatal error.
    
    
    
    


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