Your first snippet just explicitly conveys some logic that otherwise must go on behind the scenes.

I was curious as to the performance hit of invoking wantarray and scalar along with a trinary operator, as opposed to allowing the internals to take care of the decision. So I wrote a sample test that creates an array of 20,000 elements (by preextending an empty array by assigning a value to $#array).

I then wrote two functions; one with your wantarray logic and one without, put them side by side, and wrote wrapper functions for them that invoked each function twice; once in scalar and once in list context. I then used Benchmark to test.

The results were seemingly inconclusive even for such a large array, and going through 5000 iterations of the test. But then I realized that I was testing more the speed of returning an array than the speed of testing the logic. So I changed it to 50,000 iterations on an array of 1000 elements. ...and the results were... inconclusive. Or at least, the results indicated that there is no significant difference between the first and the second construct.

Update: hardburn points out that there is a flaw in my test. However I had already refined it to what I believe to be a better comparison. See the discussion in this node for the more accurate test.

Here is the code I used to test: 

use strict;
use warnings;
use Benchmark;

my @array;
$#array = 1000;

sub with_want {
    return wantarray ? @array : scalar @array;
}

sub without {
    return @array;
}

sub test_with {
    my @testary = with_want();
    my $testscalar = with_want();
}

sub test_without {
    my @testary = with_want();
    my $testscalar = with_want();
}

my $count = 50000;

timethese ( $count, {
    "With wantarray" => \&test_with,
    "Without wantarray" => \&test_without
} );

__OUTPUT__
Benchmark: timing 50000 iterations of With wantarray, Without wantarra
+y...
With wantarray: 16 wallclock secs (17.50 usr +  0.01 sys = 17.52 CPU) 
+@ 2854.70/s (n=50000)
Without wantarray: 18 wallclock secs (17.47 usr +  0.01 sys = 17.48 CP
+U) @ 2859.59/s (n=50000)

[download]

I'm far from being an expert on constructing benchmark tests. This particular test is probably still flawed in ways that I haven't considered.

But the preliminary result is that it doesn't make any difference from an efficiency standpoint which method you use.

UPDATE: Thanks hardburn for pointing out the flaw in this comparison. I would rewrite it except that I've already created a better comparison elsewhere in this thread, that more clearly demonstrates the issue. You'll find a more accurate discussion here: Re: Re: Re: returning arrays from a sub - how clever is Perl?.


Dave


"If I had my life to do over again, I'd be a plumber." -- Albert Einstein

In reply to Re: returning arrays from a sub - how clever is Perl? by davido
in thread returning arrays from a sub - how clever is Perl? by mildside

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