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For use with commands specified in and L<alienfile> or in your C<Build.Pl>
when used with L<Alien::Base::ModuleBuild>.

Helpers allow users of your Alien module to use platform or environment
determined logic to compute command names or arguments in your installer
logic.  Helpers allow you to do this without making your Alien module a
requirement when a build from source code is not necessary.

As a concrete example, consider L<Alien::gmake>, which provides the
helper C<gmake>:

 package Alien::gmake;
 
 ...
 
 sub alien_helper {
   my($class) = @_;
   return {
     gmake => sub {
       # return the executable name for GNU make,
       # usually either make or gmake depending on
       # the platform and environment
       $class->exe;
     }
   },
 }

Now consider L<Alien::nasm>.  C<nasm> requires GNU Make to build from
source code, but if the system C<nasm> package is installed we don't
need it.  From the L<alienfile> of C<Alien::nasm>:

 use alienfile;
 
 plugin 'Probe::CommandLine' => (
   command => 'nasm',
   args    => ['-v'],
   match   => qr/NASM version/,
 );
 
 share {
   ...
   plugin 'Extract' => 'tar.gz';
   plugin 'Build::MSYS';
 
   build [
     'sh configure --prefix=%{alien.install.prefix}',
     '%{gmake}',
     '%{gmake} install',
   ];
 };
 
 ...

=head2 inline_auto_include

 my(@headers) = Alien::MyLibrary->inline_auto_include;

List of header files to automatically include in inline C and C++
code when using L<Inline::C> or L<Inline::CPP>.  This is provided
as a public interface primarily so that it can be overridden at run
time.  This can also be specified in your C<Build.PL> with
L<Alien::Base::ModuleBuild> using the C<alien_inline_auto_include>
property.

=head2 runtime_prop

 my $hashref = Alien::MyLibrary->runtime_prop;

Returns a hash reference of the runtime properties computed by L<Alien::Build> during its
install process.  If the L<Alien::Base> based L<Alien> was not built using L<Alien::Build>,
then this will return undef.

=head2 alt

 my $new_alien = Alien::MyLibrary->alt($alt_name);
 my $new_alien = $old_alien->alt($alt_name);

Returns an L<Alien::Base> instance with the alternate configuration.

Some packages come with multiple libraries, and multiple C<.pc> files to
use with them.  This method can be used with C<pkg-config> plugins to
access different configurations.  (It could also be used with non-pkg-config
based packages too, though there are not as of this writing any build
time plugins that take advantage of this feature).

From your L<alienfile>

 use alienfile;
 
 plugin 'PkgConfig' => (
   pkg_name => [ 'libfoo', 'libbar', ],
 );

Then in your base class works like normal:

 package Alien::MyLibrary;
 
 use parent qw( Alien::Base );
 
 1;

Then you can use it:

 use Alien::MyLibrary;
 
 my $cflags = Alien::MyLibrary->alt('foo1')->cflags;
 my $libs   = Alien::MyLibrary->alt('foo1')->libs;

=head2 alt_names

 my @alt_names = Alien::MyLibrary->alt_names

Returns the list of all available alternative configuration names.

=head2 alt_exists

 my $bool = Alien::MyLibrary->alt_exists($alt_name)

Returns true if the given alternative configuration exists.