(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).
If you have an arg whose default is something you’re not supposed to bind as a default value in the function sig (e.g. the result of a function call), make it an Optional, default it to None, and then on the first line just do some_arg = some_arg or interesting_function()
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.
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.
classC:
def__repr__(self): return [k for k, v inglobals().items() if v is self][0]
def__bool__(self):
print(f"{self}.__bool__() was called")
returnFalse
a, b = C(), C()
print(f"result: {a or b}")
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.
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!
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.
Ruby:
a || b(no
returnas last line is returned implicitly, no semicolon)EDIT: As pointed out in the comments, this is not strictly equivalent, as it will return
bifaisfalseas well as if it’snil(these are the only two falsy values in Ruby).Python:
return a or bi 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 bThis diverges from the OP code snippets if a has the value
False.I personally dislike this because when you read “or” you expect some boolean result not a random object :/
there’s always the second option for you
In python: Not necessarily.
If you have an arg whose default is something you’re not supposed to bind as a default value in the function sig (e.g. the result of a function call), make it an
Optional, default it toNone, and then on the first line just dosome_arg = some_arg or interesting_function()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.
Not quite. If
ais not truthy, then the expressiona or bwill always returnb.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}")output
a.__bool__() was called result: bAh, good catch.
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.
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:
nilandfalse. Some other languages treat0and""(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!
Perl has both
$a || $band$a // $b.The
||version is older and has the value of$bif$ais any false value includingundef(which is pretty much Perl’snull/nil).The
//version has the value of$biff$aisundef. Other “false” values carry through.Ruby took both “no
returnrequired” 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 || 1is1in Perl but0in Ruby. Perl can0 // 1instead if the0, which is a defined value, needs to pass through.Typescript/Javascript too
Not strictly equivalent, since
||tests for truthiness, not just null.That’s fair, but it’s close enough that it functions identically
Only for the
nullcase. For other cases it doesn’t function identically, since it also treats"",0andundefinedthe same asnull.