On Fri, Jul 29, 2005 at 07:21:44PM +0200, Krzysztof Duleba wrote: > Yitzchak Scott-Thoennes wrote: > > >However code like the above does end up using twice the space; it's > >allocated once to store the result of the x operation and again when > >it's copied to $a. > > Really? I hope you're wrong. Avoiding copy operation while declaring a new > variable with a value is a very important optimization.
Patches welcome. http://perldoc.perl.org/perlhack.html There are some optimizations in this area; if you do something like: perl -we'sub foo { "a" x (1024 * 1024) } $bar = foo()' The assignment doesn't actually copy, it just replaces $bar's string buffer with the one from foo()'s return value, but I'm pretty sure returning a value from a subroutine itself involves a copy. For some operations, an assignment of the result of the operation to a lexical can be optimized away in code that looks like this: perl -we'my $foo; $foo = "bar: " . ("a" x (1024 * 1024))' Extending this to work for x is possible in principle, but complicated by the two different modes of x (list and scalar). See "Some comments about 'T'" in opcode.pl and Perl_ck_sassign in op.c in the perl source. This optimization only applies to already existing lexicals, not to ones just being declared or to package variables. In 5.9.x, there is experimental "copy on write" code that may suppress the copy in your situation. -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
