Re: if variants

One thing that's worth mentioning is that while this:

if($foo == 7) {
    print "foo is 7\n";
} else {
    print "foo is not 7\n";
}
[download]

is acceptable, this:

unless($foo != 7) {
    print "foo is 7\n";
} else {
    print "foo is not 7\n";
}
[download]

is not. Sure, perl will accept it (I consider this to be a bug in perl), and it'll run, but anyone writing it should be beaten savagely. It's VERY hard to read.

Comment on Re: if variants Select or Download Code

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Re^2: if variants by apotheon (Deacon) on Oct 20, 2004 at 18:57 UTC
I edited to include some brief mention of the undesirability of the != operator there. Thanks for the suggestion. - apotheon CopyWrite Chad Perrin	[reply]
Re^3: if variants by ihb (Deacon) on Oct 21, 2004 at 14:37 UTC
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 { ... }` [download] can be read `if (X) { ... } if (not X) { ... }` [download] "unless X" can be read "if not X". Combining this gives you `unless (X) { ... } else { ... } if (not X) { ... } if (not not X) { ... }` [download] 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.` [download] 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!	[reply] [d/l] [select]
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	[reply]
Re^3: if variants by DrHyde (Prior) on Oct 21, 2004 at 08:40 UTC
Noooooo! `!=` is fine. It's `unless ... else` that is hideously broken!	[reply] [d/l] [select]
Re^4: if variants by apotheon (Deacon) on Oct 21, 2004 at 08:46 UTC
I can understand avoiding the != in an if statement, since using unless covers that functionality. I don't know why unless . . . else would be "bad", however. Explain? - apotheon CopyWrite Chad Perrin	[reply]
Re^5: if variants by DrHyde (Prior) on Oct 22, 2004 at 09:22 UTC
Re^6: if variants by apotheon (Deacon) on Oct 23, 2004 at 09:34 UTC

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