substr is usually pretty fast: 
my $str_a = 'Foo';
my $letter = substr $str_a, 0, 1;
for my $str_b ( @list ) {
    next if $letter eq substr $str_b, 0, 1;
    expensive_function($str_a , $str_b);
}

[download]

-Mark

In reply to Re: Matching First Character of Strings Efficiently by kvale
in thread Matching First Character of Strings Efficiently by Limbic~Region

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