Allow renaming of symbols on import
# Enable renaming in Exporter
use Exporter::Renaming;
# Import File::Find::find as main::search
use File::Find Renaming => [ find => search];
# Disable renaming
no Exporter::Renaming
Allow Renaming of symbols on Import
This module adds the ability to rename symbols to the standard Exporter module. After \*(C`use Exporter::Renaming\*(C', you can import symbols from exporting modules not only under their original names, but also under names of your choosing.
Here, symbol is used to mean anything that could be exported by a Module, that is, a Perl function or variable. Thus a symbol begins with an optional type character (one of \*(C`$\*(C', \*(C`@\*(C', \*(C`%\*(C', \*(C`&\*(C', and \*(C`*\*(C'), followed by a name (a Perl identifier, made up of alphanumerics and \*(C`_\*(C', starting with a non-digit).
To trigger renaming behavior, the import list of a subsequent \*(C`use <module>\*(C' statement must begin with the keyword 'Renaming', followed by a list reference, the <renaming list|/Renaming List>, which describes the renaming imports (see below). After that, a normal import list may follow, which Exporter processes as usual.
The renaming list contains renaming pairs, which are pairs of symbols. The first part of a pair is the original symbol (as known to the exporting module) and the second one is the renamed symbol (as you want to use it after import). It is an error (fatal, as all \*(C`Renaming\*(C' or \*(C`Exporter\*(C' errors) if the renaming list has an odd number of elements, or if one of its symbols is invalid.
If none of the symbols in a renaming pair contains a type character, an \*(C`&\*(C' is assumed. If only one has a type character, this type is assumed for the other one too. If both have type characters, it is an error if they don't agree.
If the renamed symbol (the second part) of a renaming pair is undefined, the original symbol is imported unchanged, so you can include normal imports in a renaming list without retyping the name.
It is an error for a symbol to appear more than once as the second part of a renaming pair, that is, to specify the same thing twice as the target of a renaming operation. It is allowed to import the same symbol multiple times with different targets. Maybe it even makes sense in some situations.
Exporter continues to behave normally for normal imports while renaming behavior is switched on. Only the presence of the keyword \*(C`Renaming\*(C', followed by an array reference in the first and second positions after a \*(C`use\*(C' statement triggers renaming.
The renaming behavior of Exporter is thus compatible with its standard behavior. If renaming must be switched off for some reason, this can be done via \*(C`no Export::Renaming\*(C'.
If an import list contains both a renaming list and a sequence of normal import statements, the renaming is done first, as indicated by its position. No cross-check is done between the results of renaming and the normal imports, as if these resulted from two separate \*(C`use\*(C' statements.
All examples assume that
use Exporter::Renaming;
has been called (and that \*(C`no Exporter::Renaming\*(C' hasn't).
The most obvious application of \*(C`Exporter::Renaming\*(C' is to solve a name conflict. Suppose our module already defines a function \*(C`find\*(C', and we want to use the standard \*(C`File::Find\*(C' module. We could then rename \*(C`find\*(C' from \*(C`File::Find\*(C' to \*(C`search\*(C' in our own module:
use File::Find Renaming => [ find => 'search' ];
Let's assume the \*(C`finddepth\*(C' function from File::Find doesn't cause a name conflict, and we want to import it under its original name as well.
This does it in the renaming list:
use File::Find Renaming => [ find => 'search', finddepth => undef, ];
...as does this, but explicitly:
use File::Find Renaming => [ find => 'search', finddepth => 'finddepth', ];
...while this uses a regular import:
use File::Find Renaming => [ find => 'search' ], 'finddepth';
Should you find it annoying that a pedantic module author has chosen to adorn all of the module's exports with a redundant prefix (these things happen), you could do this:
use Mythical::Graphics::Module Renaming => [ gfxColor => '%color', # this imports a hash gfxPen => 'pen', gfxLine => 'line', # .... # etc ];
...lower-casing the names as well.
If you need to add clarifying prefixes that a sloppy module author has neglected to provide in the exports (these things happen), you go the other way around:
use Legendary::Graphics::Module Renaming [ Color => '%gfxColor', Pen => 'gfxPen', Line => 'gfxLine', # ... # etc ];
...also lower-casing the initial letters.
If you are confronted with a standard module that uses a slightly non-standard naming convention (it happens), you can rectify the situation:
use Data::Dumper Renaming => [ Dumper => 'dump' ];
Now you can say \*(C`print dump \ %some_hash\*(C' instead of \*(C`print Dumper ...\*(C';
As has been mentioned in section Operation, no cross-check is done between renaming exports and normal exports that go on in the same \*(C`use\*(C' statement. This means that a renaming import may later be overwritten by a normal import without a clear indication. This happens when one of the new names given in renaming coincides with one of the original ones imported through normal import.
\*(C`Exporter::Renaming\*(C' only affects modules that do standard exporting, that is, modules that inherit their \*(C`import\*(C' method from Exporter. Modules that use a different \*(C`import\*(C' method are unaffected and don't understand renaming lists.
Renaming doesn't affect the name c<caller> sees for a function. This should come as no surprise, since normal export doesn't affect this name either. It is always the (package-qualified) name the function was originally compiled with.
The lack of a cross-check between renaming and normal imports is regrettable, but unlikely to be fixed unless Renaming is made part of Exporter. Except for the simplest cases, only Exporter can parse an export list.
Calls of \*(C`use Exporter::Renaming\*(C' and \*(C`no Exporter::Renaming\*(C' don't nest. Instead of switching unconditionally, \*(C`no Renaming\*(C' should only switch off the behavior if it was off in the corresponding call to \*(C`use Exporter::Renaming\*(C'. A future release may address this.
Exporter, Perl
Anno Siegel, <[email protected]>
Thanks to Avi Finkel ([email protected]) and Simon Cozens ([email protected]) for a discussion of this project on \s-1IRC\s0. While brief, their remarks helped me think about things the right way.
Copyright 2003 by Anno Siegel
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.