just as in the 5.003 release. By default, binary compatibility
is preserved at the expense of symbol table pollution.
-=head2 Subroutine Parameters Are Not Autovivified
+=head2 Subroutine arguments created only when they're modified
-In Perl versions 5.002 and 5.003, array and hash elements used as
-subroutine parameters were "autovivified"; that is, they were brought
-into existence if they did not already exist. For example, calling
-C<func($h{foo})> would create C<$h{foo}> if it did not already exist,
-causing C<exists $h{foo}> to become true and C<keys %h> to return
-C<('foo')>.
+In Perl 5.004, nonexistent array and hash elements used as subroutine
+parameters are brought into existence only if they are actually
+assigned to (via C<@_>).
-Perl 5.004 returns to the pre-5.002 behavior of I<not> autovivifying
-array and hash elements used as subroutine parameters.
+Earlier versions of Perl vary in their handling of such arguments.
+Perl versions 5.002 and 5.003 always brought them into existence.
+Perl versions 5.000, 5.001, and 5.002 brought them into existence only
+if they were not the first argument (which was almost certainly a
+bug). Earlier versions of Perl never brought them into existence.
+
+For example, given this code:
+
+ undef @a; undef %a;
+ sub show { print $_[0] };
+ sub change { $_[0]++ };
+ show($a[2]);
+ change($a{b});
+
+After this code executes in Perl 5.004, $a{b} exists but $a[2] does
+not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
+(but $a[2]'s value would have been undefined).
=head2 Fixed Parsing of $$<digit>, &$<digit>, etc.
C<$$."0">, but rather to C<${$0}>. To get the old behavior, change
"$$" followed by a digit to "${$}".
+=head2 No Resetting of $. on Implicit Close
+
+The documentation for Perl 5.0 has always stated that C<$.> is I<not>
+reset when an already-open file handle is re-opened with no intervening
+call to C<close>. Due to a bug, perl versions 5.000 through 5.0003
+I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
+
=head2 Changes to Tainting Checks
A bug in previous versions may have failed to detect some insecure
and is implemented using the new Opcode module. Please read the new
Opcode and Safe documentation.
+=head2 Embedding Improvements
+
+In older versions of Perl it was not possible to create more than one
+Perl interpreter instance inside a single process without leaking like a
+sieve and/or crashing. The bugs that caused this behavior have all been
+fixed. However, you still must take care when embedding Perl in a C
+program. See the updated perlembed manpage for tips on how to manage
+your interpreters.
+
=head2 Internal Change: FileHandle Class Based on IO::* Classes
File handles are now stored internally as type IO::Handle. The
=item flock
-is now supported on more platforms, and prefers fcntl
-to lockf when emulating.
+is now supported on more platforms, prefers fcntl to lockf when
+emulating, and always flushes before (un)locking.
=item printf and sprintf
matches together in conjunction with ordinary matches using the C<\G>
zero-width assertion. See L<perlop> and L<perlre>.
+=item C<m//x> ignores whitespace before ?*+{}
+
+The C<m//x> construct has always been intended to ignore all unescaped
+whitespace. However, before Perl 5.004, whitespace had the effect of
+esacping repeat modifier like "*" or "?". For example, C</a *b/x> was
+(mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
+
=item nested C<sub{}> closures work now
Prior to the 5.004 release, nested anonymous functions didn't work
=item isa(CLASS)
-C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
+C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
C<isa> is also exportable and can be called as a sub with two arguments. This
allows the ability to check what a reference points to. Example:
Each unique hash key is only allocated once, no matter how many hashes
have an entry with that key. So even if you have 100 copies of the
-same hash, the hash keys never have to be re-allocated.
+same hash, the hash keys never have to be reallocated.
=head1 Pragmata
additions also make it feasible to manipulate C<HE*>s (hash entries),
which can be more efficient. See L<perlguts> for details.
-=item Embedding improvements
-
-In older versions of Perl it was not possible to create more than one
-instance of a Perl interpreter inside the same process without leaking
-like mad and/or crashing. The major bugs which caused this behavior
-have been fixed, however, you still must take care when embedding Perl
-in a C program. See the updated perlembed manpage for tips on how to
-manage your interpreters.
-
=back
=head1 Documentation Changes
projects / p5sagit/p5-mst-13.2.git / blobdiff