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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',
   ];
 };
 
 ...

=cut

sub alien_helper {
  {};
}

=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 overidden 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.

=cut

sub inline_auto_include {
  my ($class) = @_;
  return [] unless $class->config('inline_auto_include');
  $class->config('inline_auto_include')
}

sub Inline {
  my ($class, $language) = @_;
  return if $language !~ /^(C|CPP)$/;
  my $config = {
    CCFLAGSEX    => $class->cflags,
    LIBS         => $class->libs,
  };
  
  if (@{ $class->inline_auto_include } > 0) {
    $config->{AUTO_INCLUDE} = join "\n", map { "#include \"$_\"" } @{ $class->inline_auto_include };
  }
  
  $config;
}

=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.

=cut

{
  my %alien_build_config_cache;

  sub runtime_prop
  {
    my($class) = @_;
  
    return $alien_build_config_cache{$class} if
      exists $alien_build_config_cache{$class};
  
    $alien_build_config_cache{$class} ||= do {
      my $dist = ref $class ? ref $class : $class;
      $dist =~ s/::/-/g;
      my $dist_dir = eval { File::ShareDir::dist_dir($dist) };
      return if $@;
      my $alien_json = File::Spec->catfile($dist_dir, '_alien', 'alien.json');
      return unless -r $alien_json;
      open my $fh, '<', $alien_json;
      my $json = do { local $/; <$fh> };
      close $fh;
      require JSON::PP;
      my $config = JSON::PP::decode_json($json);
      $config->{distdir} = $dist_dir;