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Re^3: if variants

by ihb (Deacon)
on Oct 21, 2004 at 14:37 UTC ( #401180=note: print w/ replies, xml ) Need Help??


in reply to Re^2: if variants
in thread if variants

It's worth noting, by the way, that using $foo != 7 as the control statement in an if statement is generally a Bad Idea. The unless statement is designed to cover that need, and using the != operator there just makes the code harder to read later when it must be maintained.

I second DrHyde (Re^3: if variants). It's definately not bad and neither is it a maintenance trouble. That whole sentence above should be removed from your text. It's just plain wrong.

The unless keyword is made to make you write code more like a natural language. It's not there to take !='s place in if expressions. They can both coexist happily and be mixed however you please.

Why the combination of unless and else is shunned by many is because it's a sort of double negation.

if (X) { ... } else { ... }
can be read
if (X) { ... } if (not X) { ... }
"unless X" can be read "if not X". Combining this gives you
unless (X) { ... } else { ... } if (not X) { ... } if (not not X) { ... }
which just doesn't read well. Logically it's not strange but it's a funny and inappreciated way of expressing oneself.

My own (rather inconsistent) style is to use unless for exceptional behaviour, and if for expected/wanted behaviour. When using unless I usually want something, but something might stop me from doing that. With if I express that I perhaps want something, perhaps not.

print ... unless $quiet; # I want to print. exit if $done; # I might want to exit here. exit unless $stay; # I want to exit here, but apparently # something is holding me back.
The examples can perhaps be better, and I'm not consistant myself in my use, but that's give you an idea of how I tend to use them.

ihb

See perltoc if you don't know which perldoc to read!
Read argumentation in its context!


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Re^4: if variants
by apotheon (Deacon) on Oct 21, 2004 at 14:48 UTC
    Thanks for the clarification. Mea culpa.

    - apotheon
    CopyWrite Chad Perrin

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