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diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod index 3e78c7bd78..e8ef30f09d 100644 --- a/pod/perlsyn.pod +++ b/pod/perlsyn.pod @@ -711,6 +711,41 @@ You can change the way that an object is matched by overloading the C<~~> operator. This trumps the usual smart match semantics. See L<overload>. +=head3 Differences from Perl 6 + +The Perl 5 smart match and C<given>/C<when> constructs are not +absolutely identical to their Perl 6 analogues. The most visible +difference is that, in Perl 5, parentheses are required around +the argument to C<given()> and C<when()>. Parentheses in Perl 6 +are always optional in a control construct such as C<if()>, +C<while()>, or C<when()>; they can't be made optional in Perl +5 without a great deal of potential confusion, because Perl 5 +would parse the expression + + given $foo { + ... + } + +as though the argument to C<given> were an element of the hash +C<%foo>, interpreting the braces as hash-element syntax. + +The table of smart matches is not identical to that proposed +by the Perl 6 specification Synopsis 4. Some of the differences +are simply a consequence of Perl 5's different data model, while +other changes have been made to address problems with the Perl 6 +proposal. For example, the Perl 6 specification implies that +C<$string ~~ qr/regex/> would test string equality, rather than +doing a regular expression match. On the other hand, informal +examples elsewhere make it clear that a regular expression +match is the intended behaviour. Thus the Synopsis 4 smart +match specification cannot yet be regarded as definitive. + +In Perl 6, C<when()> will always do an implicit smart match +with its argument, whilst it is convenient in Perl 5 to +suppress this implicit smart match in certain situations, +as documented above. (The difference is largely because Perl 5 +does not, even internally, have a boolean type.) + =head2 Goto X<goto> |