Author: larry
Date: Tue Feb 5 09:55:29 2008
New Revision: 14501
Modified:
doc/trunk/design/syn/S02.pod
doc/trunk/design/syn/S03.pod
doc/trunk/design/syn/S06.pod
Log:
Added named placeholders using $:foo twigil; idea from cognominal++:
Placeholder subs can now also autoadd [EMAIL PROTECTED] or *%_ to the signature
Methods without signatures may use placeholders
Modified: doc/trunk/design/syn/S02.pod
==============================================================================
--- doc/trunk/design/syn/S02.pod (original)
+++ doc/trunk/design/syn/S02.pod Tue Feb 5 09:55:29 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 10 Aug 2004
- Last Modified: 17 Jan 2008
+ Last Modified: 5 Feb 2008
Number: 2
- Version: 126
+ Version: 127
This document summarizes Apocalypse 2, which covers small-scale
lexical items and typological issues. (These Synopses also contain
@@ -1292,7 +1292,8 @@
$foo ordinary scoping
$.foo object attribute accessor
- $^foo self-declared formal parameter
+ $^foo self-declared formal positional parameter
+ $:foo self-declared formal named parameter
$*foo global variable
$+foo contextual variable
$?foo compiler hint variable
@@ -1583,6 +1584,10 @@
my ($a, $, $c) = 1..3;
print unless (state $)++;
+Outside of declarative contexts you may use C<*> for a placeholder:
+
+ ($a, *, $c) = 1..3;
+
=item *
Ordinary package-qualified names look like in Perl 5:
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Tue Feb 5 09:55:29 2008
@@ -2791,7 +2791,7 @@
are insufficient for defining the "pecking order" of code. Note that
you can bind to either a bare block or a pointy block. Binding to a
bare block conveniently leaves the topic in C<$_>, so the final form
-above is equivalent to a C<default>. (Placeholders parameters may
+above is equivalent to a C<default>. (Placeholder parameters may
also be used in the bare block form, though of course their types
cannot be specified that way.)
Modified: doc/trunk/design/syn/S06.pod
==============================================================================
--- doc/trunk/design/syn/S06.pod (original)
+++ doc/trunk/design/syn/S06.pod Tue Feb 5 09:55:29 2008
@@ -13,9 +13,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 21 Mar 2003
- Last Modified: 2 Jan 2008
+ Last Modified: 5 Feb 2008
Number: 6
- Version: 91
+ Version: 92
This document summarizes Apocalypse 6, which covers subroutines and the
@@ -151,10 +151,15 @@
means the declared formal parameter is I<not> considered readonly; only
its elements are. See L</Parameters and arguments> below.
-Note also that if the sub's block contains placeholder variables (such
-as C<$^foo>), it is considered to have a formal signature already, so
-no implicit bindings to C<@_> or C<%_> are assumed (nor is an explicit
-signature allowed.) So in that case, this section does not apply.
+Note also that if the sub's block contains placeholder variables
+(such as C<$^foo> or C<$:bar>), those are considered to be formal
+parameters already, so in that case C<@_> or C<%_> fill the role of
+sopping up unmatched arguments. That is, if those containers are
+explicitly mentioned within the body, they are added as slurpy
+parameters. This allows you to easily customize your error message
+on unrecognized parameters. If they are not mentioned in the body,
+they are not added to the signature, and normal dispatch rules will
+simply fail if the signature cannot be bound.
=head2 Blocks
@@ -1508,25 +1513,42 @@
Even though every bare block is a closure, bare blocks can't have
explicit parameter lists. Instead, they use "placeholder" variables,
-marked by a caret (C<^>) after their sigils.
+marked by a caret (C<^>) or a colon (C<:>) after their sigils.
+The caret marks positional placeholders, while the colon marks named
+placeholders.
Using placeholders in a block defines an implicit parameter list. The
-signature is the list of distinct placeholder names, sorted in Unicode order.
-So:
+signature is the list of distinct positional placeholder names,
+sorted in Unicode order, following by the named placeholder names in
+any order. So:
- { $^y < $^z && $^x != 2 }
+ { say "woof" if $:dog; $^y < $^z && $^x != 2 }
is a shorthand for:
- -> $x,$y,$z { $y < $z && $x != 2 }
+ -> $x,$y,$z,:$dog { say "woof" if $dog; $y < $z && $x != 2 }
Note that placeholder variables syntactically cannot have type constraints.
Also, it is illegal to use placeholder variables in a block that already
has a signature, because the autogenerated signature would conflict with that.
-Placeholder names consisting of a single uppercase letter are disallowed,
+Positional placeholder names consisting of a single uppercase letter are
disallowed,
not because we're mean, but because it helps us catch references to
obsolete Perl 5 variables such as $^O.
+A function containing placeholders may also refer to either C<@_>
+or C<%_> or both, each of which (if so used) will be added to the
+signature as a normal readonly slurpy pararmeter:
+
+ { say $:what; warn "bad option: $_\n" for keys %_; }
+
+turns into
+
+ -> :$what, *%_ { say $what; warn "bad option: $_\n" for keys %_; }
+
+If not used, they are not added, and a dispatch with mispatched parameters
will fail.
+
+Placeholders may also be used in method bodies that have no formal signature.
+
=head1 Properties and traits
Compile-time properties are called "traits". The
