in reply to Simple Matching

Try 

print "[$_]:", eval "\$string =~ tr/$_//";

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Note: this may be slower than your original.

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Re^2: Simple Matching
by rnroot (Initiate) on Sep 28, 2009 at 05:04 UTC
    Thank you both. I was looking at Friedl's book on RegEx and wrapping myself up in eval's when both of you replied. Thank you. I am working on optimizing a bit of code and have not needed eval yet. Is there a workaround for this specific example, e.g., "grep -c"? Counting characters in a string should be fast and simple.
[reply]

      It's only getting compiled once, just as if it was outside of eval, so what's the problem?

      If you wanted to reuse the counter, make a sub if it: 

      $counters{$_} = eval "sub { \$_[0] =~ tr/\Q$_\E// }";

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        Thanks again, Putting the eval into Method 2 below is (much) slower than any other match (as noted by BrowserUK). Brute force (Method 3) is significantly faster than either 1 or 2, but does not let me loop through an array to check match counts. I have tried "grep -c" within perl and it works, but is not as fast as brute force. Is there a faster way? After 15+ years of Perl I have not needed to worry about cutting edge optimizing (in Perl) ... ergo my ignorance. Thanks for help again. 
        my $flush = 0;
my @suits = ( "D", "S", "C", "H" );
my $long_hand = ("2H 3D 4C 5S 5H)";

# Method 1:  43 microseconds
#    (My initial code ... seemed slow ... ergo benchmark)
foreach ( @suits ) {
    @m = ( $long_hand =~ m/$_/g );
    $flush = 1 if  ($#m eq 4 );
}

# Method 2: 126 microseconds (definitely bottleneck)
foreach ( @suits ) {
    my $count = ( eval "\$long_hand =~ tr/$_//" );
    $flush = 1 if  ($count eq 5 );
}

#Method 3: accounts for only 3(!) microseconds of code
# Ugly but functional for very few patterns to check
# BUT what if I had 10k patterns to check
$flush = 1 if ( $long_hand =~ tr/D// eq 5);
$flush = 1 if ( $long_hand =~ tr/S// eq 5);
$flush = 1 if ( $long_hand =~ tr/C// eq 5);
$flush = 1 if ( $long_hand =~ tr/H// eq 5);

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