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know the features of your language (lemmy.world)
submitted 2 years ago by to c/programmerhumor@lemmy.ml
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[–] 49 points 2 years ago* (last edited 2 years ago) (14 children)

Ruby:

a || b

(no return as last line is returned implicitly, no semicolon)

EDIT: As pointed out in the comments, this is not strictly equivalent, as it will return b if a is false as well as if it's nil (these are the only two falsy values in Ruby).

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  • [–] 22 points 2 years ago (6 children)

    Python:

    return a or b

    i like it because it reads like a sentence so it somewhat makes sense

    and you can make it more comprehensive if you want to:

    return a if a is not None else b

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  • [–] 1 point 2 years ago (2 children)

    For newer python people, they see return a or b and typically think it returns a boolean if either is True. Nope. Returns a if a is truthy and then checks if b is truthy. If neither are truthy, it returns b.

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  • [–] 7 points 2 years ago* (last edited 2 years ago) (1 child)

    Returns a if a is truthy and then checks if b is truthy. If neither are truthy, it returns b.

    Not quite. If a is not truthy, then the expression a or b will always return b.

    So, there is never any reason to check the truthiness of b.

    you can paste this in your repl to confirm it does not.

    class C:
 def __repr__(self): return [k for k, v in globals().items() if v is self][0]
 def __bool__(self):
  print(f"{self}.__bool__() was called")
  return False

a, b = C(), C()
print(f"result: {a or b}")

    spoiler output

    a.__bool__() was called
result: b

    :::

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  • [–] 13 points 2 years ago (1 child)

    This doesn't work for booleans because false is not null but also not truthy. One of things I hate about ruby is that it doesn't have a native null coalescing operator.

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  • [–] 1 point 2 years ago

    Yeah, you're quite correct, it's not exactly equivalent, I just went on auto-pilot because it's used so much for that purpose 🤖

    It's much closer to being a true null-coalescing operator than 'OR' operators in other languages though, because there's only two values that are falsy in Ruby: nil and false. Some other languages treat 0 and "" (and no doubt other things), as falsy. So this is probably the reason Ruby has never added a true null-coalescing operator, there's just much fewer cases where there's a difference.

    It's going to drive me mad now I've seen it, though 😆 That's usually the case with language features, though, you don't know what you're missing until you see it in some other language!

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  • [–] 7 points 2 years ago*

    Perl has both $a || $b and $a // $b.

    The || version is older and has the value of $b if $a is any false value including undef (which is pretty much Perl's null/nil).

    The // version has the value of $b iff $a is undef. Other "false" values carry through.

    Ruby took both "no return required" and "no final semicolon required" from Perl (if not a few other things), I think, but it seems that // was Perl later borrowing Ruby's || semantics. Interesting.

    i.e. 0 || 1 is 1 in Perl but 0 in Ruby. Perl can 0 // 1 instead if the 0, which is a defined value, needs to pass through.

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  • [–] 6 points 2 years ago (3 children)

    Typescript/Javascript too

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  • [–] 17 points 2 years ago* (last edited 2 years ago) (2 children)

    Not strictly equivalent, since || tests for truthiness, not just null.

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