Talk about $_[0] in 'as' callbacks for constant types

[perl/modules/Lexical-Types.git] / lib / Lexical / Types.pm

diff --git a/lib/Lexical/Types.pm b/lib/Lexical/Types.pm
index 841c3aad3393d64ab2117ba0b1e606479c4a1761..c5bca1e792a0621ea31e10916e0c60f68476cf8d 100644 (file)
--- a/lib/Lexical/Types.pm
+++ b/lib/Lexical/Types.pm
@@ -50,10 +50,26 @@ BEGIN {
 
 =head1 DESCRIPTION
 
-This pragma allows you to hook the execution of typed lexicals declarations (C<my Str $x>).
-In particular, it can be used to automatically tie or bless typed lexicals.
+This pragma allows you to hook the execution of typed lexicals declarations (C<my Str $x>) by calling a configurable method in a configurable package at each run.
+In particular, it can be used to automatically tie or bless typed lexicals whenever they are initialized.
 
-It is B<not> implemented with a source filter.
+Remind that for C<perl> to be able to parse C<my Str $x>, you need :
+
+=over 4
+
+=item *
+
+either the C<Str> package to be defined ;
+
+=item *
+
+or for C<Str> to be a constant sub returning a valid defined package.
+
+=back
+
+so make sure you follow one of those two strategies to define your types.
+
+This pragma is B<not> implemented with a source filter.
 
 =cut
 
@@ -109,10 +125,15 @@ or the desired package and method name, in that order (if any of those is C<unde
 
 =back
 
-=back
+Note that if the type is a constant, C<$_[0]> will be set to the I<value> of constant and not to its name.
+
+    use Lexical::Types as => sub { $_[0] => 'new' };
+    use constant Str => 'MyStr';
+    my Str $x; # calls MyStr->new
 
-The initializer method receives an alias to the pad entry of C<$x> in C<$_[1]> and the original type name (C<Str>) in C<$_[2]>.
-You can either edit C<$_[1]> in place, in which case you should return an empty list, or return a new scalar that will be copied into C<$x>.
+This means in particular that you can't both use constant types and redirect several types to different methods of the same package, because then you can't distinguish between the original types with C<$_[0]>.
+
+=back
 
 =cut
 
@@ -154,6 +175,22 @@ sub unimport {
  $^H{+(__PACKAGE__)} = undef;
 }
 
+=head1 RUN-TIME INITIALIZER METHOD
+
+The initializer method receives an alias to the pad slot of the initialized lexical in C<$_[1]> and the original type name in C<$_[2]>.
+You can either edit C<$_[1]> in place, in which case you should return an empty list, or return a new scalar that will be copied into the pad slot.
+
+    use Lexical::Types as => 'My';
+
+    my Str $x;
+
+    ...
+
+    sub My::Str::TYPEDSCALAR {
+     # $_[1] is an alias to $x, and $_[2] is 'Str'
+     ...
+    }
+
 =head1 INTEGRATION
 
 You can integrate L<Lexical::Types> in your module so that using it will provide types to your users without asking them to load either L<Lexical::Types> or the type classes manually.
@@ -193,7 +230,7 @@ or for C<Str> to be a constant sub returning a valid defined package.
 
 =back
 
-Those restrictions apply even if you use the C<'as'> option to redirect to another package, and are unlikely to find a workaround as this happens deep inside the lexer - far from the reach of an extension.
+The restrictions on the type (being either a defined package name or a constant) apply even if you use the C<'as'> option to redirect to another package, and are unlikely to find a workaround as this happens deep inside the lexer - far from the reach of an extension.
 
 Only one mangler or prefix can be in use at the same time in a given scope.