Presumably, the only thing that the double quotes would slow down is in the parse/compilation phase. After that, it is unlikely that "x" and 'x' would process any differently.

"As fast as possible" means Benchmark, of course:

Benchmark: timing 25 iterations of Double, Single...
    Double:  2 wallclock secs ( 1.57 usr +  0.01 sys =  1.58 CPU) @ 15
+.82/s (n=25)
    Single:  1 wallclock secs ( 1.57 usr +  0.01 sys =  1.58 CPU) @ 15
+.82/s (n=25)
         Rate Double Single
Double 15.8/s     --    -0%
Single 15.8/s     0%     --
[download]

Which seems to be bang on. If you introduce '$' into the characters that are used to create the random strings, there is a slight difference:

Benchmark: timing 25 iterations of Double, Single...
    Double:  3 wallclock secs ( 3.13 usr +  0.14 sys =  3.27 CPU) @  7
+.65/s (n=25)
    Single:  3 wallclock secs ( 3.18 usr +  0.06 sys =  3.24 CPU) @  7
+.72/s (n=25)
         Rate Double Single
Double 7.65/s     --    -1%
Single 7.72/s     1%     --
[download]

So it would seem that using single or double quotes, apart from functional differences, is merely style. I prefer to use double quotes almost always, except for short single-letter strings, but that's the influence of C where single quotes can only be used for single characters, and double quotes meant 'string'.

And the code for the curious:

#!/usr/bin/perl

use Benchmark qw [ cmpthese ];

my (@letter) = ('A'..'Z','a'..'z','0'..'9');
my (@single,@double);

sub RandomCrap
{
        return join ('', map { $letter[rand(@letter)] } 0..64);
}

sub Prep
{
        for (my $i = 0; $i < 5; $i++)
        {
                my $func = '@x = (';
                for (my $n = 0; $n < 1000; $n++)
                {
                        $func .= "'".RandomCrap()."',";
                }
                $func .= ')';

                push (@single, $func);
        }

        @double = map { tr/'/"/; $_ } @single;
}

sub Evalu
{
        my ($array) = @_;

        foreach my $func (@$array)
        {
                eval $func;
        }
}

Prep();

cmpthese (25,
        {
                'Single' => sub { Evalu (\@single); },
                'Double' => sub { Evalu (\@double); },
        }
);
[download]

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