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[gitmo/Moo.git] / lib / Sub / Quote.pm

package Sub::Quote;

use strictures 1;

sub _clean_eval { eval $_[0] }

use Sub::Defer;
use B 'perlstring';
use Scalar::Util qw(weaken);
use base qw(Exporter);

our $VERSION = '1.003000';
$VERSION = eval $VERSION;

our @EXPORT = qw(quote_sub unquote_sub quoted_from_sub);

our %QUOTED;

our %WEAK_REFS;

sub capture_unroll {
  my ($from, $captures, $indent) = @_;
  join(
    '',
    map {
      /^([\@\%\$])/
        or die "capture key should start with \@, \% or \$: $_";
      (' ' x $indent).qq{my ${_} = ${1}{${from}->{${\perlstring $_}}};\n};
    } keys %$captures
  );
}

sub inlinify {
  my ($code, $args, $extra, $local) = @_;
  my $do = 'do { '.($extra||'');
  if (my ($code_args, $body) = $code =~ / +my \(([^)]+)\) = \@_;(.*)$/s) {
    if ($code_args eq $args) {
      $do.$body.' }'
    } else {
      $do.'my ('.$code_args.') = ('.$args.'); '.$body.' }';
    }
  } else {
    my $assign = '';
    if ($local || $args ne '@_') {
      $assign = ($local ? 'local ' : '').'@_ = ('.$args.'); ';
    }
    $do.$assign.$code.' }';
  }
}

sub quote_sub {
  # HOLY DWIMMERY, BATMAN!
  # $name => $code => \%captures => \%options
  # $name => $code => \%captures
  # $name => $code
  # $code => \%captures => \%options
  # $code
  my $options =
    (ref($_[-1]) eq 'HASH' and ref($_[-2]) eq 'HASH')
      ? pop
      : {};
  my $captures = pop if ref($_[-1]) eq 'HASH';
  undef($captures) if $captures && !keys %$captures;
  my $code = pop;
  my $name = $_[0];
  my $quoted_info;
  my $deferred = defer_sub +($options->{no_install} ? undef : $name) => sub {
    unquote_sub($quoted_info->[4]);
  };
  $quoted_info = [ $name, $code, $captures, undef, $deferred ];
  weaken($QUOTED{$deferred} = $quoted_info);
  return $deferred;
}

sub quoted_from_sub {
  my ($sub) = @_;
  $QUOTED{$sub||''};
}

sub unquote_sub {
  my ($sub) = @_;
  unless ($QUOTED{$sub}[3]) {
    my ($name, $code, $captures) = @{$QUOTED{$sub}};

    my $make_sub = "{\n";

    my %captures = $captures ? %$captures : ();
    $captures{'$_QUOTED'} = \$QUOTED{$sub};
    $make_sub .= capture_unroll("\$_[1]", \%captures, 2);

    $make_sub .= (
      $name
          # disable the 'variable $x will not stay shared' warning since
          # we're not letting it escape from this scope anyway so there's
          # nothing trying to share it
        ? "  no warnings 'closure';\n  sub ${name} {\n"
        : "  \$_QUOTED->[3] = sub {\n"
    );
    $make_sub .= $code;
    $make_sub .= "  }".($name ? '' : ';')."\n";
    if ($name) {
      $make_sub .= "  \$_QUOTED->[3] = \\&${name}\n";
    }
    $make_sub .= "}\n1;\n";
    $ENV{SUB_QUOTE_DEBUG} && warn $make_sub;
    {
      local $@;
      no strict 'refs';
      local *{$name} if $name;
      unless (_clean_eval $make_sub, \%captures) {
        die "Eval went very, very wrong:\n\n${make_sub}\n\n$@";
      }
    }
  }
  $QUOTED{$sub}[3];
}

sub CLONE {
  %QUOTED = map { defined $_ ? ($_->[4] => $_) : () } values %QUOTED;
  weaken($_) for values %QUOTED;
}

1;

=head1 NAME

Sub::Quote - efficient generation of subroutines via string eval

=head1 SYNOPSIS

 package Silly;

 use Sub::Quote qw(quote_sub unquote_sub quoted_from_sub);

 quote_sub 'Silly::kitty', q{ print "meow" };

 quote_sub 'Silly::doggy', q{ print "woof" };

 my $sound = 0;

 quote_sub 'Silly::dagron',
   q{ print ++$sound % 2 ? 'burninate' : 'roar' },
   { '$sound' => \$sound };

And elsewhere:

 Silly->kitty;  # meow
 Silly->doggy;  # woof
 Silly->dagron; # burninate
 Silly->dagron; # roar
 Silly->dagron; # burninate

=head1 DESCRIPTION

This package provides performant ways to generate subroutines from strings.

=head1 SUBROUTINES

=head2 quote_sub

 my $coderef = quote_sub 'Foo::bar', q{ print $x++ . "\n" }, { '$x' => \0 };

Arguments: ?$name, $code, ?\%captures, ?\%options

C<$name> is the subroutine where the coderef will be installed.

C<$code> is a string that will be turned into code.

C<\%captures> is a hashref of variables that will be made available to the
code.  See the L</SYNOPSIS>'s C<Silly::dagron> for an example using captures.

=head3 options

=over 2

=item * no_install

B<Boolean>.  Set this option to not install the generated coderef into the
passed subroutine name on undefer.

=back

=head2 unquote_sub

 my $coderef = unquote_sub $sub;

Forcibly replace subroutine with actual code.

If $sub is not a quoted sub, this is a no-op.

=head2 quoted_from_sub

 my $data = quoted_from_sub $sub;

 my ($name, $code, $captures, $compiled_sub) = @$data;

Returns original arguments to quote_sub, plus the compiled version if this
sub has already been unquoted.

Note that $sub can be either the original quoted version or the compiled
version for convenience.

=head2 inlinify

 my $prelude = capture_unroll '$captures', {
   '$x' => 1,
   '$y' => 2,
 };

 my $inlined_code = inlinify q{
   my ($x, $y) = @_;

   print $x + $y . "\n";
 }, '$x, $y', $prelude;

Takes a string of code, a string of arguments, a string of code which acts as a
"prelude", and a B<Boolean> representing whether or not to localize the
arguments.

=head2 capture_unroll

 my $prelude = capture_unroll '$captures', {
   '$x' => 1,
   '$y' => 2,
 }, 4;

Arguments: $from, \%captures, $indent

Generates a snippet of code which is suitable to be used as a prelude for
L</inlinify>.  C<$from> is a string will be used as a hashref in the resulting
code.  The keys of C<%captures> are the names of the variables and the values
are ignored.  C<$indent> is the number of spaces to indent the result by.

=head1 CAVEATS

Much of this is just string-based code-generation, and as a result, a few caveats
apply.

=head2 return

Calling C<return> from a quote_sub'ed sub will not likely do what you intend.
Instead of returning from the code you defined in C<quote_sub>, it will return
from the overall function it is composited into.

So when you pass in:

   quote_sub q{  return 1 if $condition; $morecode }

It might turn up in the intended context as follows:

  sub foo {

    <important code a>
    do {
      return 1 if $condition;
      $morecode
    };
    <important code b>

  }

Which will obviously return from foo, when all you meant to do was return from
the code context in quote_sub and proceed with running important code b.

=head2 strictures

Sub::Quote compiles quoted subs in an environment where C<< use strictures >>
is in effect. L<strictures> enables L<strict> and FATAL L<warnings>.

The following dies I<< Use of uninitialized value in print... >>

 no warnings;
 quote_sub 'Silly::kitty', q{ print undef };

If you need to disable parts of strictures, do it within the quoted sub:

 quote_sub 'Silly::kitty', q{ no warnings; print undef };

=head1 SUPPORT

See L<Moo> for support and contact information.

=head1 AUTHORS

See L<Moo> for authors.

=head1 COPYRIGHT AND LICENSE

See L<Moo> for the copyright and license.