Re: array overhead

$a=[@$a] can be used to shrink the array. (Well, create a new one the minimal size.)

$ perl -MDevel::Peek -e'push @$a, $_ for qw( a b c d e ); Dump($a,1); 
+$a=[@$a]; Dump($a,1);'
SV = IV(0x817bc44) at 0x817bc48
  REFCNT = 1
  FLAGS = (ROK)
  RV = 0x816c158
  SV = PVAV(0x816d1c8) at 0x816c158
    REFCNT = 1
    FLAGS = ()
    ARRAY = 0x8177928
    FILL = 4                       <-----  5 visible elements
    MAX = 11                       <----- 12 elements allocated
    ARYLEN = 0x0
    FLAGS = (REAL)
SV = IV(0x817bc44) at 0x817bc48
  REFCNT = 1
  FLAGS = (ROK)
  RV = 0x816cea8
  SV = PVAV(0x816d1dc) at 0x816cea8
    REFCNT = 1
    FLAGS = ()
    ARRAY = 0x8183cb8
    FILL = 4                       <-----  5 visible elements
    MAX = 4                        <-----  5 elements allocated
    ARYLEN = 0x0
    FLAGS = (REAL)
[download]

But you might only end up fragmenting your memory, leaving less usable free memory behind.

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Re^2: array overhead by dave_the_m (Monsignor) on Jan 06, 2011 at 00:15 UTC
Yeah, 232 byes is a lot of overhead for an array. My back-of-the envelope calculations show a clean, minimal array should have an overhead of about 60 bytes on a 32-bit system, so that shrinking should make a difference. I doubt that fragmentation will be an issue. The OP probably wants to shrink the SV holding the integer value too, since it appears to be 56 bytes, so probably still holds a string too (`$a[5] = int $[a5]` should do it). Dave.	[reply] [d/l]
Re^3: array overhead by ikegami (Patriarch) on Jan 06, 2011 at 17:41 UTC
Assigning a number to a scalar doesn't free the string buffer, it just marks it as unused. You "solution" can actually increase the memory used. `$ perl -MDevel::Size=total_size -E' $a[5]="5678"; say total_size($a[5]); $x=int($a[5]); say total_size($a[5]); ' 40 44` [download] `undef $s` (but not `$s = undef;`) will free the string buffer. `$ perl -MDevel::Size=total_size -E' $a[5]="5678"; say total_size($a[5]); $t=int($a[5]); undef $a[5]; $a[5]=$t; say total_size($a[5]); ' 40 36` [download] It doesn't downgrade the scalar from PVIV to IV, though. You'd need to start with a new scalar to do that. `$ perl -MDevel::Peek -MDevel::Size=total_size -E' $a[5]="5678"; say total_size($a[5]); $t=int($a[5]); delete $a[5]; $a[5]=$t; say total_size($a[5]); ' 40 16` [download]	[reply] [d/l] [select]
Re^4: array overhead by dave_the_m (Monsignor) on Jan 06, 2011 at 19:57 UTC
Yeah sorry, bad example. I was thinking in terms of using it within in your `$a=[@$a]`, e.g. `$a= [ @$a[0..4], int($a->[5]) ]`, where it would get a new SV. Dave.	[reply] [d/l] [select]