"I am not a fan of this policy :)"

There seems little point to it. There is a very slight compile time speed penalty to double-quoted strings. This benchmark demonstrates that:

use Benchmark ':all';

cmpthese(250_000, {
    e_double => sub { eval q{"foo"} },
    e_single => sub { eval q{'foo'} },
});

[download]

But at runtime, there's no difference, as they compile to the same optree...

$ perl -MO=Concise -e'$x=q{foo}' > single.txt
-e syntax OK
$ perl -MO=Concise -e'$x=qq{foo}' > double.txt
-e syntax OK
$ diff -s single.txt double.txt
Files single.txt and double.txt are identical
$ rm single.txt double.txt

[download]

That is not always the case in all programming languages though. The PHP compiler is less smart than the Perl compiler, so in PHP there's a real speed penalty on double-quoted strings...

<?php

class Bench {
    public $name;
    protected $_start;
    protected $_finish;
    
    public function __construct ($name) {
        $this->name = $name;
    }

    public function start () {
        if ($this->_start) die("already started");
        $this->_start = microtime(true);
    }

    public function finish () {
        if ($this->_finish) die("already finished");
        $this->_finish = microtime(true);
    }
    
    public function total_time () {
        return $this->_finish - $this->_start;
    }
    
    public function run ($callable, $count=1) {
        $this->start();
        for ($i = 0; $i < $count; $i++)
            call_user_func($callable);
        $this->finish();
    }
    
    public function __toString () {
        return sprintf("%s: %0.6f s", $this->name, $this->total_time()
+);
    }
    
    public static function cmpthese ($iterations, $tests) {
        foreach ($tests as $name => $code) {
            $bench = new Bench ($name);
            $bench->run($code, $iterations);
            $per_second = $iterations / $bench->total_time();
            printf("%s: %0.2f /s\n", $bench->name, $per_second);
        }
    }
}

Bench::cmpthese(100000, array(
    "single quotes" => create_function('', 'return \'foo\';'),
    "double quotes" => create_function('', 'return "foo";'),
));

[download]
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^2: Perl::Critic and Subroutines by tobyink
in thread Perl::Critic and Subroutines by daugh016

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