/ 
Import-Base-1.004
River stage two • 9 direct dependents • 13 total dependents
/ Import::Base

NAME

Import::Base - Import a set of modules into the calling module

VERSION

version 1.004

SYNOPSIS

### Static API
package My::Base;
use parent 'Import::Base';

# Modules that are always imported
our @IMPORT_MODULES = (
    'strict',
    'warnings',
    # Import only these subs
    'My::Exporter' => [ 'foo', 'bar', 'baz' ],
    # Disable uninitialized warnings
    '-warnings' => [qw( uninitialized )],
    # Test for minimum version
    { 'Getopt::Long' => 2.31 },
    # Callback to generate modules to import
    sub {
        my ( $bundles, $args ) = @_;
        return "My::MoreModule" => [qw( fuzz )];
    },
);

# Optional bundles
our %IMPORT_BUNDLES = (
    with_signatures => [
        'feature' => [qw( signatures )],
        # Put this last to make sure nobody else can re-enable this warning
        '>-warnings' => [qw( experimental::signatures )]
    ],
    Test => [qw( Test::More Test::Deep )],
    Class => [
        # Put this first so we can override what it enables later
        '<Moo',
    ],
);

### Consumer classes
# Use only the default set of modules
use My::Base;

# Use one of the optional packages
use My::Base 'with_signatures';
use My::Base 'Test';
use My::Base 'Class';

# Exclude some modules and symbols we don't want
use My::Base -exclude => [ 'warnings', 'My::Exporter' => [ 'bar' ] ];

DESCRIPTION

This module makes it easier to build and manage a base set of imports. Rather than importing a dozen modules in each of your project's modules, you simply import one module and get all the other modules you want. This reduces your module boilerplate from 12 lines to 1.

USAGE

Base Module

Creating a base module means extending Import::Base and creating an @IMPORT_MODULES package variable with a list of modules to import, optionally with a arrayref of arguments to be passed to the module's import() method.

A common base module should probably include strict, warnings, and a feature set.

package My::Base;
use parent 'Import::Base';

our @IMPORT_MODULES = (
    'strict',
    'warnings',
    feature => [qw( :5.14 )],
);

Now we can consume our base module by doing:

package My::Module;
use My::Base;

Which is equivalent to:

package My::Module;
use strict;
use warnings;
use feature qw( :5.14 );

Now when we want to change our feature set, we only need to edit one file!

Import Bundles

In addition to a set of modules, we can also create optional bundles with the %IMPORT_BUNDLES package variable.

package My::Bundles;
use parent 'My::Base';

# Modules that will always be included
our @IMPORT_MODULES
    experimental => [qw( signatures )],
);

# Named bundles to include
our %IMPORT_BUNDLES = (
    Class => [qw( Moose MooseX::Types )],
    Role => [qw( Moose::Role MooseX::Types )],
    Test => [qw( Test::More Test::Deep )],
);

Now we can choose one or more bundles to include:

# lib/MyClass.pm
use My::Base 'Class';

# t/mytest.t
use My::Base 'Test';

# t/lib/MyTest.pm
use My::Base 'Test', 'Class';

Bundles must always come before options. Bundle names cannot start with "-".

Extended Base Module

We can further extend our base module to create more specialized modules for classes and testing.

package My::Class;
use parent 'My::Base';
our @IMPORT_MODULES = (
    'Moo::Lax',
    'Types::Standard' => [qw( :all )],
);

package My::Test;
use parent 'My::Base';
our @IMPORT_MODULES = (
    'Test::More',
    'Test::Deep',
    'Test::Exception',
    'Test::Differences',
);

Now all our classes just need to use My::Class and all our test scripts just need to use My::Test.

NOTE: Be careful when extending base modules from other projects! If the module you are extending changes, your modules may unexpectedly break. It is best to keep your base modules on a per-project scale.

Unimporting

Sometimes instead of use Module we need to do no Module, to turn off strict or warnings categories for example.

By prefixing the module name with a -, Import::Base will act like no instead of use.

package My::Base;
use parent 'Import::Base';
our @IMPORT_MODULES = (
    'strict',
    'warnings',
    feature => [qw( :5.20 signatures )],
    '-warnings' => [qw( experimental::signatures )],
);

Now the warnings for using the 5.20 subroutine signatures feature will be disabled.

Version Check

The standard Perl use function allows for a version check at compile time to ensure that a module is at least a minimum version.

# Require Getopt::Long version 2.31 or higher
use Getopt::Long 2.31;

Generally, you should be declaring your dependency with the correct version, but some modules (like Getopt::Long) change their behavior based on what version you ask for.

To ask for a specific version, use a hashref with the key is the module and the value as the required version.

our @IMPORT_MODULES = (
    # Require a minimum version
    { 'Getopt::Long' => 2.31 },
    # Version and imports
    { 'File::Spec::Functions' => 3.47 } => [qw( catfile )],
);

-exclude

When importing a base module, you can use -exclude to prevent certain modules or symbols from being imported (if, for example, they would conflict with existing symbols).

# Prevent the "warnings" module from being imported
use My::Base -exclude => [ 'warnings' ];

# Prevent the "bar" sub from My::Exporter from being imported
use My::Base -exclude => [ 'My::Exporter' => [ 'bar' ] ];

NOTE: If you find yourself using -exclude often, you would be better off removing the module or sub and creating a bundle, or only including it in those modules that need it.

Control Ordering

The order you import modules can be important!

use warnings;
no warnings 'uninitialized';
# Uninitialized warnings are disabled

no warnings 'uninitialized';
use warnings;
# Uninitialized warnings are enabled!

Due to modules enforcing their own strict and warnings, like Moose and Moo, you may not even know it's happening. This can make it hard to disable the experimental warnings:

use feature qw( postderef );
no warnings 'experimental::postderef';
use Moo;
# The postderef warnings are back on!

To force a module to the front or the back of the list of imports, you can prefix the module name with < or >.

package My::Base;
use parent 'Import::Base';
our @IMPORT_MODULES = (
    feature => [qw( postderef )],
    # Disable this warning last!
    '>-warnings' => [qw( experimental::postderef )],
);

our %IMPORT_BUNDLES = (
    Class => [
        # Import this module first!
        '<Moo',
    ],
);

package main;
use My::Base 'Class';
my @foo = [ 1, 2, 3 ]->@*; # postderef!

In this case, either putting Moo first or putting no warnings 'experimental::postderef' last would solve the problem.

NOTE: < and > come before -.

If you need even more control over the order, consider the "Dynamic API".

Subref Callbacks

To get a little bit of dynamic support in the otherwise static module lists, you may add sub references to generate module imports.

package My::Base;
use parent 'Import::Base';
our @IMPORT_MODULES = (
    sub {
        my ( $bundles, $args ) = @_;
        return (
            qw( strict warnings ),
            feature => [qw( :5.20 )],
        );
    },
);

# strict, warnings, and 5.20 features will be imported

Plain strings are module names. Array references are arguments to import.

NOTE: Subrefs cannot return modules with < or > to control ordering. Subrefs are run after the order has already been determined, while the imports are being executed. Subrefs can assume that imports before them have already been completed.

Subref Arguments

Sub references get an arrayref of bundles being requested, and a hashref of extra arguments. Arguments from the calling side start with a '-'. Arguments from Import::Base do not. Possible arguments are:

package         - The package we are exporting to
-exclude        - The exclusions, see L</"-exclude">.

Using package, a subref could check or alter @ISA, work with the object's metaclass (if you're using one), or export additional symbols not set up for export.

Here's an example for applying a role (Moo::Role, Role::Tiny, Moose::Role, and anything that uses with) when importing a bundle:

package My::Base;
use parent 'Import::Base';
our %IMPORT_BUNDLES = (
    'Plugin' => [
        'Moo',
        # Plugins require the "My::Plugin" role
        sub {
            my ( $bundles, $args ) = @_;
            $args->{package}->can( 'with' )->( 'My::Plugin' );
            return;
        },
    ],
);

package My::Custom::Plugin;
use My::Base 'Plugin';

NOTE: This sub is still being called during the compile phase. If you need your role to be applied later, if you get errors when trying to apply it at compile time, use the import_bundle method, below.

Custom Arguments

When using "Subref Callbacks", you can add additional arguments to the use line. The arguments list starts after the first key that starts with a '-'. To avoid conflicting with any future Import::Base feature, prefix all your custom arguments with '--'.

use My::Base -exclude => [qw( strict )], --custom => "arguments";
# Subrefs will get $args{--custom} set to "arguments"

Dynamic API

Instead of providing @IMPORT_MODULES and %IMPORT_BUNDLES, you can override the modules() method to do anything you want.

package My::Bundles;
use parent 'My::Base';

sub modules {
    my ( $class, $bundles, $args ) = @_;

    # Modules that will always be included
    my @modules = (
        experimental => [qw( signatures )],
    );

    # Named bundles to include
    my %bundles = (
        Class => [qw( Moose MooseX::Types )],
        Role => [qw( Moose::Role MooseX::Types )],
        Test => [qw( Test::More Test::Deep )],
    );

    # Go to our parent class first
    return $class->SUPER::modules( $bundles, $args ),
        # Then the always included modules
        @modules,
        # Then the bundles we asked for
        map { @{ $bundles{ $_ } } } grep { exists $bundles{ $_ } } @$bundles;
}

Using the above boilerplate will ensure that you start with all the basic functionality.

One advantage the dynamic API has is the ability to remove modules from superclasses, or completely control the order that modules are imported, even from superclasses.

Exporting symbols from the base class

Import::Base inherits from Exporter and allows for EXPORT_OK usage.

package My::Base;
use parent 'Import::Base';

our @EXPORT_OK = qw($joy);

our @IMPORT_MODULES = (
    'strict',
    'warnings',
    feature => [qw( :5.10 )],
    'My::Base' => [qw( $joy )],
);

our $joy = "Is everywhere";

package main;

use My::Base;

say $joy;

Notice how the base class 'My::Base' is in it's own IMPORT_MODULES definition.

METHODS

modules( $bundles, $args )

Prepare the list of modules to import. $bundles is an array ref of bundles, if any. $args is a hash ref of generic arguments, if any.

Returns a list of MODULE => [ import() args ]. MODULE may appear multiple times.

import_bundle( @bundles, @args )

Import a bundle at runtime. This method takes the exact same arguments as in the use My::Base ... compile-time API, but allows it to happen at runtime, so that all of the current package's subs have been made available, and all BEGIN blocks have been executed.

This is useful when using bundles to apply roles that have dependencies or other esoteric use-cases. It is not necessary for most things.

DOCUMENTATION BOILERPLATE

Here is an example for documenting your own base modules

=head1 SYNOPSIS

    package MyModule;
    use My::Base;

    use My::Base 'Class';
    use My::Base 'Role';
    use My::Base 'Test';

=head1 DESCRIPTION

This is the base module that all {{PROJECT}} files should use.

This module always imports the following into your namespace:

=over

=item L<strict>

=item L<warnings>

=item L<feature>

Currently the 5.20 feature bundle

=item L<experimental> 'signatures' 'postderef'

We are using the 5.20 experimental signatures and postfix deref syntax.

=back

=head1 BUNDLES

The following bundles are available. You may import one or more of these by name.

=head2 Class

The class bundle makes your package into a class and includes:

=over 4

=item L<Moo::Lax>

=item L<Types::Standard> ':all'

=back

=head2 Role

The role bundle makes your package into a role and includes:

=over 4

=item L<Moo::Role::Lax>

=item L<Types::Standard> ':all'

=back

=head2 Test

The test bundle includes:

=over 4

=item L<Test::More>

=item L<Test::Deep>

=item L<Test::Differences>

=item L<Test::Exception>

=back

=head1 SEE ALSO

=over

=item L<Import::Base>

=back

BEST PRACTICES

One Per Project

Every project of at least medium size should have its own base module. Consolidating a bunch of common base modules into a single distribution and releasing to CPAN may sound like a good idea, but it opens you up to difficult-to-diagnose problems.

If many projects all depend on the same base, any change to the central base module could potentially break one of the consuming modules. In a single, well-tested project, it is easy to track down and address issues due to changes in the base module. If the base module is released to CPAN, breakage may not appear until someone tries to install a module that depends on your base.

Version incompatibility, where project Foo depends on version 1 of the base, while project Bar depends on version 2, will create very frustrating situations for your users.

Having to track down another project to figure out what modules are active in the current package is a lot of work, creating frustration for contributing authors.

KNOWN ISSUES

Moo::Role does not work if base module shares the same file as role package

When trying to import Moo::Role using Import::Base, the role will not be applied if it shares the same file as the Import::Base module. For safety and sanity, you should keep your Import::Base module separate from classes and roles.

Dancer plugins do not work when applied with Import::Base

Dancer plugins check, at compile time, to see if they can be imported into the consuming class by looking for the Dancer DSL. Because Import::Base uses Module::Runtime to load the class, Dancer::Plugin thinks Module::Runtime is the calling class, sees there is no DSL to register itself with, and bails.

This issue was fixed in Dancer2 v0.200000 (released 2016-05-31). See https://github.com/PerlDancer/Dancer2/pull/1136 for more information.

SEE ALSO

Import::Into

The module that provides the functionality to create this module. If Import::Base doesn't do what you want, look at Import::Into to build your own.

Importer

This module wraps the import method of other modules, allowing you to rename the symbols you import. If you need to change a name, use this module together with Import::Base.

perl5

This module is very similar, and has a bunch of built-in bundles and features for quickly importing Perl feature sets. It is also flexible, allowing you to specify your own module bundles.

ToolSet

ToolSet is very similar. Its API just uses package methods instead of package variables. It also allows for exporting symbols directly from the bundle.

sanity

Sanity is more consise, but not as flexible. If you don't need the wild flexibility of Import::Base or the above solutions, take a look.

Toolkit

This one requires configuration files in a home directory, so is not shippable.

rig

This one also requires configuration files in a home directory, so is not shippable.

AUTHOR

Doug Bell <preaction@cpan.org>

CONTRIBUTORS

  • Brian Medley <pub-github@bmedley.org>

  • Dan Book <grinnz@gmail.com>

  • Doug Bell <doug@preaction.me>

COPYRIGHT AND LICENSE

This software is copyright (c) 2017 by Doug Bell.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.