Re^4: Avoiding silly programming mistakes


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Re^4: Avoiding silly programming mistakes

by JavaFan (Canon)

on Aug 20, 2008 at 14:11 UTC ( [id://705517]=note: print w/replies, xml )

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in thread Avoiding silly programming mistakes

All your example have a declaration in the test; so it seems more likely you want to do the assignment than the comparison.

However, Perl doesn't warn on

    if ($foo = foo()) {...}
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This is actually a common idiom, so it would be wrong for Perl to warn. Note that swapping the arguments around won't help you either:

    if (foo() = $foo) {...}
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may be valid (if foo() returns an lvalue). And whether it's valid or not is something you only know at run time - at compile time Perl cannot know whether foo returns an lvalue or not. So at best, you get a run-time error.

And if you want to compare two variables, there's no defense against mistyping '==' as '=', as both if ($foo = $bar) and if ($foo == $bar) is common.

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Re^5: Avoiding silly programming mistakes
by Limbic~Region (Chancellor) on Aug 20, 2008 at 14:48 UTC

JavaFan

I was showing that perl doesn't issue a warning any time it sees an assignment in a conditional - only when it makes sense. This was intended for others reading along, not for you since you obviously know what you are talking about.

This is actually a common idiom, so it would be wrong for Perl to warn. Note that swapping the arguments around won't help you either: ... may be valid (if foo() returns an lvalue).

Yep, exactly what I said. Perl assumes you know what you are doing and when flipping operands, an error would happen unless there was an lvalue at play.

Cheers - L~R

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