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know the features of your language (lemmy.world)
submitted 2 years ago by jroid8@lemmy.world to c/programmerhumor@lemmy.ml
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[-] zero_gravitas@aussie.zone 47 points 2 years ago* (last edited 2 years ago)

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).

[-] stebo02@sopuli.xyz 23 points 2 years ago

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

[-] Turun@feddit.de 15 points 2 years ago* (last edited 2 years ago)

This diverges from the OP code snippets if a has the value False.

[-] alehc@lemmy.world 8 points 2 years ago

I personally dislike this because when you read "or" you expect some boolean result not a random object :/

[-] stebo02@sopuli.xyz 4 points 2 years ago

there's always the second option for you

[-] rwhitisissle@lemmy.ml 2 points 2 years ago

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.

[-] cypherpunks@lemmy.ml 7 points 2 years ago* (last edited 2 years ago)

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

:::

[-] rwhitisissle@lemmy.ml 3 points 2 years ago

Ah, good catch.

[-] Witchfire@lemmy.world 7 points 2 years ago

Typescript/Javascript too

[-] FooBarrington@lemmy.world 17 points 2 years ago* (last edited 2 years ago)

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

[-] Witchfire@lemmy.world 1 points 2 years ago

That's fair, but it's close enough that it functions identically

[-] FooBarrington@lemmy.world 4 points 2 years ago

Only for the null case. For other cases it doesn't function identically, since it also treats "", 0 and undefined the same as null.

[-] palordrolap@kbin.social 7 points 2 years ago* (last edited 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.

this post was submitted on 08 Dec 2023
637 points (100.0% liked)

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