If you're operating on a single string of a few dozen/hundred/thousand characters, the difference between s///g and tr/// will not be detectable.

Sorry, but that simply isn't true.

For a 3 character string tr/// takes 1/3rd the time of starting up the regex engine.

For a 30 character string, it is 1/8th the time.

And by the time you get to just 300 characters, the regex engine is already 20 times slower for this task. 

$n = 1e0; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
       Rate    b    a
b 1000796/s   -- -60%
a 2493375/s 149%   --

$n = 1e1; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
       Rate    b    a
b  234727/s   -- -87%
a 1838169/s 683%   --

$n = 1e2; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
      Rate     b     a
b  28926/s    --  -95%

a 585631/s 1925%    --
$n = 1e3; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y];],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g;] 
};;
     Rate     b     a
b  3087/s    --  -96%
a 76540/s 2379%    --

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In reply to Re^4: Combining regexes by BrowserUk
in thread Combining regexes by davies

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