Re^4: unless versus if ( ! ) inside a subroutine

Conditionals are not always evaluated. The compiler can sometimes decide to phrase things differently.

U:\> perl -MO=Deparse -le "$x = 5; if ($x) { print $x }"
$x = 5;
if ($x) {
    print $x;
}
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U:\>perl -MO=Deparse -le "$x = 5; if (0) { print $x }"
$x = 5;
'???';
[download]

U:\>perl -MO=Deparse -le "$x = 5; if (1) { print $x }"
$x = 5;
print $x;;
[download]

U:\>perl -MO=Deparse -le "$x = 5; if (! 0) { print $x }"
$x = 5;
print $x;;
[download]

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Re^5: unless versus if ( ! ) inside a subroutine by almut (Canon) on Jan 16, 2008 at 15:11 UTC
Sure, but in those cases, constants are being tested in the conditional, which allows the compiler to make optimisations. In the OP's example, though, `$v` is a regular (mutable) scalar variable, which could change its value at runtime (after the compiler has done its work)...	[reply] [d/l]