If you even declare a variable, it would be nonsensical to warn when you assign to it. It's more the other way round: 
if (my $x) { ... }

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(variable declaration in a conditional without assignment) could actually warn, because it will never be true. (But perl intentionally doesn't have such warnings, some people like stuff like if (0) { ... }).

In reply to Re^4: Avoiding silly programming mistakes by moritz
in thread Avoiding silly programming mistakes by missingthepoint

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