oracular (3) Import::Into.3pm.gz
NAME
Import::Into - Import packages into other packages
SYNOPSIS
package My::MultiExporter;
use Import::Into;
# simple
sub import {
Thing1->import::into(scalar caller);
}
# multiple
sub import {
my $target = caller;
Thing1->import::into($target);
Thing2->import::into($target, qw(import arguments));
}
# by level
sub import {
Thing1->import::into(1);
}
# with exporter
use base qw(Exporter);
sub import {
shift->export_to_level(1);
Thing1->import::into(1);
}
# no My::MultiExporter == no Thing1
sub unimport {
Thing1->unimport::out_of(scalar caller);
}
People wanting to re-export your module should also be using Import::Into. Any exporter or pragma will
work seamlessly.
Note: You do not need to make any changes to Thing1 to be able to call "import::into" on it. This is a
global method, and is callable on any package (and in fact on any object as well, although it's rarer
that you'd want to do that).
DESCRIPTION
Writing exporters is a pain. Some use Exporter, some use Sub::Exporter, some use Moose::Exporter, some
use Exporter::Declare ... and some things are pragmas.
Exporting on someone else's behalf is harder. The exporters don't provide a consistent API for this, and
pragmas need to have their import method called directly, since they effect the current unit of
compilation.
"Import::Into" provides global methods to make this painless.
METHODS
$package->import::into( $target, @arguments );
A global method, callable on any package. Loads and imports the given package into $target. @arguments
are passed along to the package's import method.
$target can be an package name to export to, an integer for the caller level to export to, or a hashref
with the following options:
package
The target package to export to.
filename
The apparent filename to export to. Some exporting modules, such as autodie or strictures, care
about the filename they are being imported to.
line
The apparent line number to export to. To be combined with the "filename" option.
level
The caller level to export to. This will automatically populate the "package", "filename", and
"line" options, making it the easiest most constent option.
version
A version number to check for the module. The equivalent of specifying the version number on a "use"
line.
$package->unimport::out_of( $target, @arguments );
Equivalent to "import::into", but dispatches to $package's "unimport" method instead of "import".
WHY USE THIS MODULE
The APIs for exporting modules aren't consistent. Exporter subclasses provide export_to_level, but if
they overrode their import method all bets are off. Sub::Exporter provides an into parameter but
figuring out something used it isn't trivial. Pragmas need to have their "import" method called directly
since they affect the current unit of compilation.
It's ... annoying.
However, there is an approach that actually works for all of these types.
eval "package $target; use $thing;"
will work for anything checking caller, which is everything except pragmas. But it doesn't work for
pragmas - pragmas need:
$thing->import;
because they're designed to affect the code currently being compiled - so within an eval, that's the
scope of the eval itself, not the module that just "use"d you - so
sub import {
eval "use strict;"
}
doesn't do what you wanted, but
sub import {
strict->import;
}
will apply strict to the calling file correctly.
Of course, now you have two new problems - first, that you still need to know if something's a pragma,
and second that you can't use either of these approaches alone on something like Moose or Moo that's both
an exporter and a pragma.
So, a solution for that is:
use Module::Runtime;
my $sub = eval "package $target; sub { use_module(shift)->import(\@_) }";
$sub->($thing, @import_args);
which means that import is called from the right place for pragmas to take effect, and from the right
package for caller checking to work - and so behaves correctly for all types of exporter, for pragmas,
and for hybrids.
Additionally, some import routines check the filename they are being imported to. This can be dealt with
by generating a #line directive in the eval, which will change what "caller" reports for the filename
when called in the importer. The filename and line number to use in the directive then need to be fetched
using "caller":
my ($target, $file, $line) = caller(1);
my $sub = eval qq{
package $target;
#line $line "$file"
sub { use_module(shift)->import(\@_) }
};
$sub->($thing, @import_args);
And you need to switch between these implementations depending on if you are targeting a specific
package, or something in your call stack.
Remembering all this, however, is excessively irritating. So I wrote a module so I didn't have to
anymore. Loading Import::Into creates a global method "import::into" which you can call on any package to
import it into another package. So now you can simply write:
use Import::Into;
$thing->import::into($target, @import_args);
This works because of how perl resolves method calls - a call to a simple method name is resolved against
the package of the class or object, so
$thing->method_name(@args);
is roughly equivalent to:
my $code_ref = $thing->can('method_name');
$code_ref->($thing, @args);
while if a "::" is found, the lookup is made relative to the package name (i.e. everything before the
last "::") so
$thing->Package::Name::method_name(@args);
is roughly equivalent to:
my $code_ref = Package::Name->can('method_name');
$code_ref->($thing, @args);
So since Import::Into defines a method "into" in package "import" the syntax reliably calls that.
For more craziness of this order, have a look at the article I wrote at
<http://shadow.cat/blog/matt-s-trout/madness-with-methods> which covers coderef abuse and the "${\...}"
syntax.
And that's it.
SEE ALSO
I gave a lightning talk on this module (and curry and Safe::Isa) at YAPC::NA 2013
<https://www.youtube.com/watch?v=wFXWV2yY7gE&t=46m05s>.
ACKNOWLEDGEMENTS
Thanks to Getty for asking "how can I get "use strict; use warnings;" turned on for all consumers of my
code?" and then "why is this not a module?!".
AUTHOR
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
CONTRIBUTORS
haarg - Graham Knop (cpan:HAARG) <haarg@haarg.org> Mithaldu - Christian Walde (cpan:MITHALDU) <walde.christian@gmail.com>
COPYRIGHT
Copyright (c) 2012 the Import::Into "AUTHOR" and "CONTRIBUTORS" as listed above.
LICENSE
This library is free software and may be distributed under the same terms as perl itself.