Provided by: libbadger-perl_0.16-2_all 
NAME
Badger::Exporter - symbol exporter
SYNOPSIS
Defining a module subclassed from Badger::Exporter:
package Badger::AnyModule;
use base 'Badger::Exporter';
our ($WIZ, $BANG, @BING, %BONG);
Specifying the exports using the all-in-one "exports()" method:
__PACKAGE__->exports(
all => '$WIZ $BANG', # like Exporter's @EXPORT
any => '@BING %BONG', # like @EXPORT_OK
tags => { # like %EXPORT_TAGS
foobar => 'foo bar',
},
hooks => { # custom hooks
hello => sub {
print "Hello World!\n"
},
},
fail => sub { # handle unknown exports
print "I'm sorry Dave, I can't do that.\n"
},
before => sub { # pre-import hook
my ($class, $target, $symbols) = @_;
print "This gets run before the import\n"
},
after => sub { # post-import hook
my ($class, $target) = @_;
print "This gets run after the import\n"
},
);
Or individual "export_XXX()" methods:
# export all these symbols by default # methods can take either
__PACKAGE__->export_all(qw( $WIZ $BANG )); # a list of symbols or a
__PACKAGE__->export_all('$WIZ $BANG'); # space-delimited string
# export these symbols if requested
__PACKAGE__->export_any(qw( @BING %BONG )); # list
__PACKAGE__->export_any('@BING %BONG'); # string
# define sets of symbols for export
__PACKAGE__->export_tags(
set1 => [ qw( $WIZ $BANG ) ], # list
set2 => '@BING %BONG', # string
set3 => 'foo bar', # string
set4 => { # hash
# use hash ref to define aliases for symbols
foo => '&the_foo_sub',
bar => '&the_bar_sub',
},
);
# define hooks for import symbols
__PACKAGE__->export_hooks(
hello => sub {
my ($class, $target, $symbol, $more_symbols) = @_;
print $symbol, " ", shift(@$more_symbols), "\n";
}
);
# define generic hooks to run before/after import
__PACKAGE__->export_before(
sub {
my ($class, $target, $symbols) = @_;
print "This gets run before the import\n"
}
);
__PACKAGE__->export_after(
sub {
my ($class, $target) = @_;
print "This gets run after the import\n"
}
);
# define catch-all for any failed import symbols
__PACKAGE__->export_fail(
sub {
my ($class, $target, $symbol, $more_symbols) = @_;
warn "Cannot export $symbol from $class to $target\n";
}
);
Using the module:
package main;
# imports default items: $WIZ $BANG
use Badger::AnyModule;
# import specific items
use Badger::AnyModule qw( $WIZ @BING );
# import user-defined sets
use Badger::AnyModule qw( :set1 :set3 );
# specifying the :default set ($WIZ $BANG) and others
use Badger::AnyModule qw( :default @BING );
# importing all symbols using the :all set
use Badger::AnyModule ':all';
# specifying multiple symbols in a single string
use Badger::AnyModule ':set1 $WIZ @BING';
# triggering import hooks: prints "hello world\n";
use Badger::AnyModule
hello => 'world';
# import hooks and other items
use Badger::AnyModule
hello => 'world',
qw( @BING %BONG );
# import fail hook gets called for any unknown symbols
use Badger::AnyModule 'badger';
# warns: Cannot export badger from Badger::AnyModule to main
# imports indicates that all remaining arguments are symbols to
# import, bypassing any hooks
use Badger::AnyModule
hello => 'world'
imports => qw( @BING %BONG );
# import (singular) option indicates that the next item is an
# import symbols (or multiple symbols in a single string) and
# disables hooks for that item only.
use Badger::AnyModule
import => '@BING %BONG';
DESCRIPTION
This module performs the same basic function as the "Exporter" module in that it exports
symbols from one package namespace to another.
Howevever, unlike the "Exporter" module it also accounts for object inheritance. If your
base class module defines a set of exportable symbols then any subclasses derived from it
will also have that same set of symbols (and any others it adds) available for export.
It implements a number of methods that simplify the process of defining what symbols can
be exported, and provides a convenient mechanism for handling special import flags.
METHODS
These methods can be used to declare the symbols that a module exports.
exports(%exports)
This all-in-one methods accepts a reference to a hash array, or a list of named parameters
and forwards the arguments onto the relevant method(s).
__PACKAGE__->exports(
all => '$WIZ $BANG', # like Exporter's @EXPORT
any => '@BING %BONG', # like @EXPORT_OK
tags => { # like %EXPORT_TAGS
foobar => 'foo bar',
},
hooks => { # custom hooks
hello => sub {
print "Hello World!\n"
},
},
fail => sub { # handle unknown exports
print "I'm sorry Dave, I can't do that.\n"
},
);
Each key corresponds to one of the methods below, specified without the "export_" prefix.
e.g. "all" for export_all(), "any" for export_any() and so on. The method is called with
the corresponding value being passed as an argument.
export_all(@symbols)
Adds all the symbols passed as arguments to the list of items that are exported by
default. This is equivalent to setting the @EXPORT package variable when using the
"Exporter" module.
__PACKAGE__->export_all('$WIZ $BANG');
Symbols can be specified as a a string of space-delimited tokens, as a list of items, or
by reference to a list of items.
__PACKAGE__->export_all('$WIZ $BANG'); # string
__PACKAGE__->export_all(qw( $WIZ $BANG )); # list
__PACKAGE__->export_all([qw( $WIZ $BANG )]); # list ref
These symbols will be imported when the module is loaded.
use Badger::AnyModule; # import $WIZ and $BANG
This behaviour can be overridden by specifying an explicit list of imported symbols.
use Badger::AnyModule '$BANG'; # $BANG only
use Badger::AnyModule '$BANG @BONG'; # $BANG and @BONG
If you specify a single string of items to export then it will be split on whitespace or a
comma+whitespace combination of characters to extract multiple symbol names from the
string. The following three examples all do the same thing. The last two are effectively
identical in all but syntax.
use Badger::AnyModule '$BANG @BONG'; # single string
use Badger::AnyModule '$BANG' '@BONG'; # two strings
use Badger::AnyModule qw($BANG @BONG); # same as above
Note that symbol splitting occurs when you specify a single string. If you specify
multiple strings then none are split.
# this doesn't work
use Badger::AnyModule '$WIZ' '$BANG $BONG'; # WRONG!
Specify an empty list of arguments if you don't want any symbols imported.
use Badger::AnyModule qw(); # imports nothing
export_any(@symbols)
Adds all the symbols passed as arguments to the list of items that are exported on
request. This is equivalent to setting the @EXPORT_OK package variable when using the
"Exporter" module.
__PACKAGE__->export_any(qw( $WIZ $BANG ));
Symbols can be specified as a space-delimited string, a list, or by reference to a list,
as per export_all().
The symbols specified as arguments are imported when the module is loaded.
use Badger::AnyModule '$BANG'; # $BANG only
use Badger::AnyModule '$BANG @BONG'; # $BANG and @BONG
use Badger::AnyModule qw($BANG @BONG); # $BANG and @BONG
export_tags(%tagsets)
Define one or more sets of symbols. This is equivalent to setting the %EXPORT_TAGS
package variable when using the "Exporter" module.
If a symbol appears in a tag set then it is assumed to be safe to export. You don't need
to explicitly call export_any() because the export_tags() method does it for you.
__PACKAGE__->export_tags(
set1 => [ qw( $WIZ $BANG ) ],
set2 => [ qw( @BING %BONG ) ],
set3 => [ qw( foo bar ) ],
);
The values in the hash array can be specified as references to lists, or space-delimited
strings.
__PACKAGE__->export_tags(
set1 => '$WIZ $BANG',
set2 => '@BING %BONG',
set3 => 'foo bar',
);
To load a set of symbols, specify the tag name with a '":"' prefix.
use Badger::AnyModule ':set1';
use Badger::AnyModule ':set1 :set2';
use Badger::AnyModule qw(:set1 :set2);
The special '":all"' set imports all symbols.
use Badger::AnyModule ':all';
The special '":default"' set imports the default set of symbols.
use Badger::AnyModule ':default @BONG';
You can also use the "export_tags()" method to define a hash array mapping aliases to
symbols.
__PACKAGE__->export_tags(
set4 => {
# use hash ref to define aliases for symbols
foo => '&the_foo_sub',
bar => '&the_bar_sub',
}
);
When this tagset is imported, the symbols identified by the values in the hash reference
(&the_foo_sub and &the_bar_sub) are exported into the caller's package as the symbols
named in the corresponding keys.
use Badger::AnyModule ':set4';
foo(); # Badger::AnyModule::the_foo_sub()
bar(); # Badger::AnyModule::the_bar_sub()
When defining a tagset with a hash reference, you can provide direct references to
subroutines instead of symbol names.
__PACKAGE__->export_tags(
set5 => {
# use hash ref to define aliases for subroutines
foo => \&the_foo_sub,
bar => \&the_bar_sub,
}
);
You can also explicitly specify the package name for a symbol:
__PACKAGE__->export_tags(
set6 => {
foo => 'Badger::Example::One::foo',
bar => '&Badger:Example::One::bar',
'$X' => '$Badger::Example::Two:X',
'$Y' => '$Badger::Example::Two:Y',
}
);
The "Badger::Exporter" module also recognises the "=" pseudo-sigil which can be used to
define constant values.
__PACKAGE__->export_tags(
set7 => {
e => '=2.718',
pi => '=3.142',
phi => '=1.618',
}
);
When this tag set is imported, "Badger::Exporter" will define constant subroutines to
represent the imported values.
use Badger::AnyModule ':set7';
print e; # 2.718
print pi; # 3.142
print phi; # 1.618
export_hooks(%hooks)
Defines one or more handlers that are invoked when particular import symbols are
specified.
__PACKAGE__->export_hooks(
hello => sub {
my ($class, $target, $symbol, $more_symbols) = @_;
print $symbol, " ", shift(@$more_symbols), "\n";
}
);
This would be used like so:
use Badger::AnyModule hello => 'world', qw( $WIZ $BANG );
The handler is passed four arguments. The first is the package name of the exporting class
(e.g. "Badger::AnyModule"). The second argument is the package name of the target class
which wants to import the symbol (e.g. "main"). The symbol itself ('"hello"' in this
case) is passed as the third argument. The final argument is a reference to a list of
remaining symbols ("['world', '$WIZ', '$BANG']").
This example shifts off the next symbol ('"world"') and prints the message to the screen
(for debugging purposes only - your handler will most likely do something more useful).
The handler may remove any number of symbols from the $more_symbols list to indicate that
they have been successfully handled. Any symbols left in the $more_symbols list will
continue to be imported as usual.
You can also define export hooks as an array reference. The code reference should be the
first item in the array. The second item is the number of arguments it expects. These will
be shifted off the $more_symbols list (automatically raising an error if one or more
values are missing or undefined) and passed as separate arguments to your handler. The
$more_symbols reference will be passed as the final argument.
__PACKAGE__->export_hooks(
example => [ \&my_export_hook, 2 ],
);
sub my_export_hook {
my ($self, $target, $symbol, $arg1, $arg2, $more_symbols) = @_;
# your code...
}
Hooks expressed this way will have closures created around them on demand by the
export_hook_generator() method. Don't worry if that doesn't mean anything much to you.
It simply means that we can delay doing any extra preparation work until we're sure that
it's going to be used.
export_before(\&handler)
This method can be called to register a handler that will be called immediately before the
exporter starts importing symbols. The handler is passed three arguments: the exporter
class, the target class, and a reference to a list of symbols that are being imported.
The handler can modify the list of symbols to change what does or doesn't get imported.
__PACKAGE__->export_before(
sub {
my ($class, $target, $symbols) = @_;
print "About to import symbols: ", join(', ', @$symbols), "\n";
}
);
Multiple handlers can be defined, either in the same class or inherited from base classes.
Handlers defined in base classes are called before those in derived classes. Multiple
handlers defined in the same class will be called in the order that they were defined in.
export_after(\&handler)
This method can be called to register a handler that will be called immediately after the
exporter has finished importing symbols. The handler is passed two arguments: the
exporter class and target class.
__PACKAGE__->export_after(
sub {
my ($class, $target) = @_;
print "Finished exporting\n";
}
);
Multiple handlers can be defined, as per export_before().
export_fail(\&handler)
This method can be used to register a subroutine to handle any export failures. The
arguments passed are as per export_hooks(). The method should return 1 to indicate that
the symbol was handled without error, or 0 to indicate failure which is then reported in
the usual way.
__PACKAGE__->export_fail(
sub {
my ($class, $target, $symbol, $more_symbols) = @_;
if ($symbol eq 'badger') {
print "OK, we'll let you import a badger\n";
return 1;
}
else {
print "You cannot import $symbol from $class into $target\n";
return 0;
}
}
);
An "export_fail" handler may also remove symbols from the $more_symbols list to indicate
that they have been handled, as per "export_hooks()".
INTERNAL METHODS
These methods are used internally to export symbols.
import(@symbols)
This is the method automatically called by Perl when a module is loaded via "use". It
delegates to the export() method.
export($package,@symbols)
This is the main method for exporting symbols.
exportables()
This methods collects and collates the values of the various package variables that
control the exporter ("EXPORT_ALL", "EXPORT_ANY", etc). It returns a reference to an
array containing:
[\@all, \%any, \%tags, \%hooks, \@fails];
This array reference is cached in the "EXPORTABLES" package variable for future use.
export_symbol($package,$symbol,$coderef)
This method can be used to install a code reference as a symbol in a package.
Badger::Exporter->export_symbol('My::Package', 'Foo', \&foosub);
export_hook_generator($name,\&code,$nargs)
This method is used to generate a closure (a fancy way of saying "wrapper subroutine")
around an existing export hook subroutine. Bare naked export hooks are typically written
like this:
sub code {
my ($self, $target, $symbol, $more_symbols) = @_
# your code...
}
Your code is responsible for shifting any arguments it expects off the front of the
$more_symbols list. It should also being doing all the messy stuff like making sure the
$more_symbols list contains enough arguments and that they're all set to defined values.
But I bet you forget sometimes, don't you? That's OK, it's easily done.
The purpose of the "export_hook_generator()" method is to simplify argument processing so
that hooks can be specified as:
[\&my_code, $nargs]
and written as:
sub code {
my (
$self, $target, $symbol, # the usual first three items
$arg1, $arg2, ..., $argn, # your $nargs items
$more_symbols # the remaining items
) = @_
}
The method should be called like something like this:
my $hook = Badger::Exporter->export_hook_generator(
'wibble', \&code, 2
);
The first argument should be the name of the option that the hook is being generated for.
This is used to report any argument errors, e.g.
Missing value for the 'wibble' option (2 wanted, 1 available)
Or:
Missing value for the 'wibble' option (argument 2 of 2 is undefined)
The second argument is a reference to your handler subroutine. The third argument is the
number of additional arguments your subroutine expects.
PACKAGE VARIABLES
AUTHOR
Andy Wardley <http://wardley.org/>
COPYRIGHT
Copyright (C) 1996-2009 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.