That will not work stand-alone because (as moritz said) use is executed at compile time. Even if placed in a BEGIN block.
For example, on Windows:
use strict;
use warnings; 

if ($^O ne "MSWin32") { use POSIX; }

local $, = "\n";
print keys %INC

[download]
shows that POSIX.pm is loaded.

In reply to Re^2: Mulit-Platform use case by cdarke
in thread Mulit-Platform use case by gokuraku

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