Re^9: Does @{ } copy arrays?

I consider my example to pass $#a as an argument an extremely common case

While I disagree about the commonness of passing $#a, there are options if it is deemed to be too slow.

$#a as an arg is an lvalue. Users can pass 0+$#a if they want the extra speed of an rvalue.
$#a as an arg is an rvalue. Users can use ${ \$#a } if they want an lvalue.

$#a as an arg is a delayed lvalue. I don't know if the mechanism can be extended to $#a, but hash element lookups are like this:

$ perl -le'\$h{k}; print exists($h{k})?1:0'
1

$ perl -le'sub{ $x=$_[0] }->($h{k}); print exists($h{k})?1:0'
0

$ perl -le'sub{ $_[0]=$x }->($h{k}); print exists($h{k})?1:0'
1

$ perl -le'sub{ $x=$_[0] }->(@h{k}); print exists($h{k})?1:0'
1

$ perl -le'sub{ $_[0]=$x }->(@h{k}); print exists($h{k})?1:0'
1
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Re^10: Does @{ } copy arrays? by BrowserUk (Patriarch) on Oct 23, 2009 at 22:22 UTC
Unfortunately, none of those 'remedies' work: C:\test>p1 [0] Perl> use Devel::Size qw[ size total_size ];; [0] Perl> @a = 1 .. 10;; [0] Perl> print size( \@a ), ':', total_size( \@a );; 256 : 496 [0] Perl> print $#a;; 9 [0] Perl> print size( \@a ), ':', total_size( \@a );; 440 : 680 C:\test>p1 [0] Perl> use Devel::Size qw[ size total_size ];; [0] Perl> @a = 1 .. 10;; [0] Perl> print size( \@a ), ':', total_size( \@a );; 256 : 496 [0] Perl> $x = 0+$#a;; [0] Perl> print size( \@a ), ':', total_size( \@a );; 432 : 672 C:\test>p1 [0] Perl> use Devel::Size qw[ size total_size ];; [0] Perl> @a = 1 .. 10;; [0] Perl> print size( \@a ), ':', total_size( \@a );; 256 : 496 [0] Perl> $x = ${ \$#a };; [0] Perl> print size( \@a ), ':', total_size( \@a );; 432 : 672 [download] In every case, the mere mention of $#a has already caused the damage to be done. Trading 76-bytes per array to save 4-bytes per array does not make sense. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. RIP PCW It is as I've been saying!(Audio until 20090817)	[reply] [d/l]
Re^11: Does @{ } copy arrays? by ikegami (Patriarch) on Oct 23, 2009 at 22:56 UTC
In every case, the mere mention of $#a has already caused the damage to be done. As I've already mentioned, we're talking about a Perl that's fixed to not add the magic for rvalue `$#a`.	[reply] [d/l]
Re^10: Does @{ } copy arrays? by LanX (Saint) on Oct 23, 2009 at 20:33 UTC
Hmm ... as far as I understood dave, copying to an rvalue doesn't help, because the array has already been "prepared" for later modification without taking care about any rvalue context !(?) so calling with arg `@a-1` is always the fastest alternative. Cheers Rolf	[reply] [d/l]
Re^11: Does @{ } copy arrays? by ikegami (Patriarch) on Oct 23, 2009 at 20:45 UTC
because the array has already been "prepared" for later modification without taking care about any rvalue context ! What? We're talking about a Perl that's fixed to not add the magic for rvalue `$#a`. You said it would be easy to forget `foo($#a)` is an lvalue and that it's a common occurrence. I replied that it's no biggie if it's true. That case can be handled if there is a need.	[reply] [d/l] [select]