Re: String concatenation

This is probably a case of unnecessary optimization, but here are benchmark results for those interested:

             s/iter         join          dot interpolate1 interpolate
+2
join           2.22           --         -24%         -25%         -32
+%
dot            1.69          31%           --          -1%         -11
+%
interpolate1   1.67          33%           1%           --         -10
+%
interpolate2   1.50          48%          13%          12%           -
+-
[download]

And here's the code that generated this. I had to loop a bunch to get any kind of result. Not sure if this has any kind of effect on anything.

use strict;
use warnings;

use Benchmark qw/:all/;

my $string;

my ($var1, $var2, $var3) = ('asdf', 'zxcv', 'qwer');

cmpthese(4, {
    dot => sub {
        $string = $var1 . $var2 . $var3 for (0 .. 10000000);
    },  
    interpolate1 => sub {
        $string = "${var1}${var2}${var3}" for (0 .. 10000000);
    },  
    interpolate2 => sub {
        $string = "$var1$var2$var3" for (0 .. 10000000);
    },  
    join => sub {
        $string = join('', $var1, $var2, $var3) for (0 .. 10000000);
    },  
});
[download]

Comment on Re: String concatenation Select or Download Code

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Re^2: String concatenation by chromatic (Archbishop) on Apr 11, 2012 at 20:31 UTC
Both of the interpolation forms compile to the same optree. Perl does the same work for both of them. Any difference between their benchmarks is noise. Given that, the time difference between concatenation and interpolation (which do have different optrees) is insignificant.	[reply]
Re^3: String concatenation by dave_the_m (Monsignor) on Apr 11, 2012 at 20:57 UTC
In fact it goes further than that; the dot form also compiles to the same optree as the interpolation forms. Dave.	[reply]
Re^4: String concatenation by JavaFan (Canon) on Apr 11, 2012 at 21:22 UTC
Hmmm. $ perl -MO=Terse -e '$v1.$v2.$v3' LISTOP (0x9dc5fe0) leave [1] OP (0x9dc6768) enter COP (0x9dd0650) nextstate BINOP (0x9dd06e0) concat [2] BINOP (0x9dd05b0) concat [1] UNOP (0x9dd0688) null [15] SVOP (0x9dd07e8) gvsv GV (0x9dcaa30) v1 UNOP (0x9dd0578) null [15] SVOP (0x9dd0630) gvsv GV (0x9dcaa58) v2 UNOP (0x9dd05d0) null [15] SVOP (0x9dcf9e0) gvsv GV (0x9dcaae4) v3 -e syntax OK $ perl -MO=Terse -e '"$v1$v2$v3"' LISTOP (0x8b92778) leave [1] OP (0x8b88768) enter COP (0x8b92650) nextstate UNOP (0x8b926e0) null [67] OP (0x8b918d0) null [3] BINOP (0x8b925d0) concat [2] BINOP (0x8b925b0) concat [1] UNOP (0x8b92688) null [15] SVOP (0x8b927e8) gvsv GV (0x8b8ca44) v1 UNOP (0x8b92578) null [15] SVOP (0x8b92630) gvsv GV (0x8b8cb34) v2 UNOP (0x8b91920) null [15] SVOP (0x8b91a10) gvsv GV (0x8b8cae4) v3 -e syntax OK [download] Similar, but subtle differences.	[reply] [d/l]
Re^5: String concatenation by Eliya (Vicar) on Apr 11, 2012 at 21:35 UTC
Re^3: String concatenation by Riales (Hermit) on Apr 11, 2012 at 20:37 UTC
Ah, yes--I ran my script a couple more times and it seems that the two interpolates and the dot are pretty much the same but the join is consistently slower. I envy the monks with an understanding of what Perl does internally!	[reply]
Re^4: String concatenation by JavaFan (Canon) on Apr 11, 2012 at 21:26 UTC
I envy the monks with an understanding of what Perl does internally! You don't need an understanding of what Perl does internally to find out whether two code snippets compile to the same optree. Use `-MO=Terse` (or `-MO=Concise`).	[reply] [d/l] [select]