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Export-These-v0.2.1
River stage two • 8 direct dependents • 10 total dependents
++
/ Export::These

NAME

Export::These - Terse Module Configuration and Symbol (Re)Exporting

SYNOPSIS

Take a fine package, exporting subroutines,

  package My::ModA;

  use Export::These "dog", "cat", ":colors"=>[qw<blue green>];

  sub dog {...}  
  sub cat {...} 
  sub blue {...} 
  sub green {...}
  1;

Another package which would like to reexport the subs from My::ModA:

  package My::ModB;
  use My::ModA;

  use Export::These ":colors"=>["more_colours"];

  sub _reexport {
    my ($packate, $target, @names)=@_;
    My::ModA->import(":colours") if grep /:colours/, @names;
  }
 
  sub more_colours { ....  }
  1;

Use package like usual:

  use My::ModB qw<:colors dog>

  # suburtines blue, green , more_colors and dog  imported

Also can use to pass in configuration information to a module:

  package My::ModB;

  use Export::These;

  sub _preexport {
    
    my @refs=grep ref, @_;
    my @non_ref= grep !ref, @_;
    
    # Use @refs as configuration data
    
    @non_ref;
  }


  # Import the module, with configuration data
  use My::ModB {option1=>"hello"}, "symbol";

  ...

DESCRIPTION

A module to make exporting symbols less verbose and more powerful. Facilitate reexporting and filtering of symbols from dependencies with minimal input from the module author. Also provide the ability to pass in 'config data' data to a module during import.

By default listing a symbol for export, even in a group/tag, means it will be automatically marked as 'export_ok', saving on duplication and managing two separate lists.

It DOES NOT inherit from Exporter nor does it utilise the import routine from Exporter. It injects its own import subroutine into the each calling package. This injected subroutine adds the desired symbols to the target package as you would expect.

If the exporting package has a _preexport subroutine, it is called as a filter 'hook' prior to normal 'importing' to allow module wide configuration or pre processing of requested import list. The return from this subroutine will be the arguments used at subsequent stages so remember to return an appropriate list.

If the exporting package has a _reexport subroutine, it is called after normal importing. This is the 'hook' location where its safe to call ->import on any dependencies modules it might want to export. The symbols from these packages will automatically be installed into the target package with no extra configuration needed.

Any reference types specified in an import are ignored during the normal import process. This allows custom module configuration to be passed during import and processed in the _preexport and _reexport hooks.

Finally, warnings about symbols redefinition in the export process (i.e. exporting to two subroutines with the same name into the same namespace) are silenced to keep warning noise to a minimum. The last symbol definition will ultimately be the one used.

MOTIVATION

Suppose you have a server module, which uses a configuration module to process configuration data. However the main program (which imported the server module) also needs to use the subroutines from the configuration module. The consumer of the server module has to also add the configuration module as a dependency.

With this module the server can simply reexport the required configuration routines, injecting the dependency, instead of the consumer hard coding it.

USAGE

Importing a module which uses this module

Importing is like normal:

    require My::Module;
    My::Moudle->import;

    use My::Moudle qw<:tag_name name2 ...>;

However, from v0.2.1 modules exporting with Export::These can also take reference values as a key without error. This allows passing non names as configuration data for the module to use:

    eg

      # Config module and export named symbols
      use My::Module {prefork=>1, workers=>10}, "symname1", ":group1",['more', 'config'];

      # Config module and export default symbols
      use My::Module {prefork=>1, workers=>10};

      # Config module only. No symbol export
      use My::Module {prefork=>1, workers=>10}, undef;

In this hypothetical example, the My::Module uses the hash and array ref as configuration internally, and the normal scalars as the symbols/tag groups to export. In the last case the undef value forces no importing of default symbols when using a reference value.

Specifying Symbols to Export

    use Export::These ...;

The pragma takes a list of arguments to add to the @EXPORT and EXPORT_OK variables. The items are taken as a name of a symbol or tag, unless the following argument in the list is an array ref.

    eg:

      use Export::These qw<sym1 sym2>;

If the item name is "export_ok", then the items in the following array ref are added to the @EXPORT_OK variable.

    eg
      use Export::These export_ok=>[qw<sym1>];

If the item name is "export", then the items in the following array ref are added to the @EXPORT_OK and the EXPORT variables. This is the same as simply listing the items at the top level.

    eg 

      use Export::These export=>[qw<sym1>];
      # same as
      # use Export::These qw<sym1>;

If the item name is "export_pass", then the items in the following array ref symbols will be allowed to be requested for import even if the module does not export them directly. Use an empty array ref to allow any names for reexporting:

    eg 

      # Allow sym1 to be reexported from sub modules
      use Export::These export_pass=>[qw<sym1>];

      # Allow any name to be reexported from submodules
      use Export::These export_pass=>[];

If the item has any other name, it is a tag name and the items in the following array ref are added to the %EXPORT_TAGS variable and to @EXPORT_OK

    eg use Export::These group1=>["sym1"];

The list can contain any combination of the above:

    eq use Export::These "sym1", group1=>["sym2", "sym3"], export_ok=>"sym4";

Rexporting Symbols

If a subroutine called _reexport exists in the exporting package, it will be called on (with the -> notation) during import, after the normal symbols have been processed. The first argument is the package name of exporter, the second is the package name of the importer (the target), and the remaining arguments are the names of symbols or tags to import.

In this subroutine, you call import on as any packages you want to reexport:

  eg 
  use Sub::Module;
  use Another::Mod;

  sub _reexport {
    my ($package, $target, @names)=@_;

    Sub::Module->import;
    Another::Mod->import(@names);
    ...
  }

Conditional Reexporting

If you would only like to require and export on certain conditions, some extra steps are needed to ensure correct setup of back end variables. Namely the $Exporter::ExportLevel variable needs to be localized and set to 0 inside a block BEFORE calling the ->import subroutine on the package.

  sub _reexport {
    my ($package, $target, @names)=@_;

    if(SOME_CONDITION){
      {
        # In an localised block, reset the export level
        local $Exporter::ExportLevel=0;
        require Sub::Module;
        require Another::Module;
      }

      Sub::Module->import;
      Another::Mod->import(@names);

    }
  }

Reexport Super Class Symbols

Any exported symbols from the inheritance chain can be reexported in the same manner, as long as they are package subroutines and not methods:

  eg 

    package ModChild;
    parent ModParent;

      # or
      
    class ModChild :isa(ModParent)

    
    sub _reexport {
      my ($package, $target, @names)=@_;
      $package->SUPER::import(@names);
    }

COMPARISON TO OTHER MODULES

Import::Into Provides clean way to reexport symbols, though you will have to roll your own 'normal' export of symbols from you own package.

Import::Base Requires a custom package to group the imports and reexports them. This is a different approach and might better suit your needs.

Reexporting symbols with Exporter directly is a little cumbersome. You either need to import everything into you module name space (even if you don't need it) and then reexport from there. Alternatively you can import directly into a package, but you need to know at what level in the call stack it is. This is exactly what this module addresses.

REPOSITOTY and BUGS

Please report and feature requests or bugs via the github repo:

https://github.com/drclaw1394/perl-export-these.git

AUTHOR

Ruben Westerberg, <drclaw@mac.com>

COPYRIGHT AND LICENSE

Copyright (C) 2023 by Ruben Westerberg

Licensed under MIT

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.