OK, I just made up a quick test case:

use strict;
use warnings;
use Benchmark 'cmpthese';

cmpthese(10000, {
    'eval'   => sub { eval_code() },
    'noeval' => sub { no_eval_code() },,
});

sub eval_code {
    my $x = 0;
    for (1..1000) {
        eval {
            $x+=1;
        }
    }
}

sub no_eval_code {
    my $x = 0;
    for (1..1000) {
        $x+=1;
    }
}
[download]

And, unless I've missed something blindingly obvious, in this trivial case there is quite an overheard with eval:

         Rate   eval noeval
eval   1495/s     --   -62%
noeval 3953/s   164%     --
[download]

But let's tweak that for a real life example. Here's some code where it "dies" one time in ten:

use strict;
use warnings;
use Benchmark 'cmpthese';

cmpthese(1000000, {
    'eval'   => sub { eval_code() },
    'noeval' => sub { no_eval_code() },,
});


sub eval_code {
    my $x = 0;
    for (reverse 0..9) {
        eval {
            my $x = 100/$_;
        };
        if ($@) {
            error_sub();
        }
    }
}

sub no_eval_code {
    for (reverse 0..9) {
        if ($_==0) {
            error_sub();
        }
        else {
            my $x = 100/$_;
        }
    }
}
[download]

and here's the benchmark results:

           Rate   eval noeval
eval    67797/s     --   -39%
noeval 111111/s    64%     --
[download]

Well. That's still significantly faster. So have I proved eval slows things down, or is this a case specific example that someone can find a counter-example for? I've been bitten by benchmarks on code snippets before, so I'm still wary of this result. Hmmmmm....

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