Updated Kernel#Rational

[sampersand]

Updated Kernel#Rational to be more accurate.

Phew, this one is a mess. In "normal operation," the signature would look like this:

type num = Complex|Float|int|_ToR|String
def self?.Rational: (num numer, num denom, exception: false) -> Rational?
                  | (num numer, num denom, ?exception: bool) -> Rational

However, Kernel#Rational also tries to be a "division operator" for some reason: If the first argument is Numeric, but defines neither to_int nor to_i nor even to_r, Kernel#Rational will return arg1 / arg2. That is, it'll actually call the / operator on the first argument, with the second.

But it gets worse. If the second argument is exactly 1, then / won't even be called.

In neither case does exception: false actually work—unlike the other conversion methods, exceptions are not caught when Kernel#Rational is trying to act like a division operator.

[ParadoxV5]

type num = Complex|Float|int|_ToR|String

Complex, Float and String are already _ToRs. So is the Integer part of int, but not necessarily the _ToInt part. So num can simply be _ToInt|_ToR.

[sampersand]

updated to take that into account

[ParadoxV5]

that’s quick … I was looking at the changes and it didn’t quite match your desc 😄

EDIT: Why force-push tho

[ParadoxV5]

However, Kernel#Rational also tries to be a "division operator" for some reason: If the first argument is Numeric, but defines neither to_int nor to_i nor even to_r, Kernel#Rational will return arg1 / arg2. That is, it'll actually call the / operator on the first argument, with the second.

Returns x/y or arg as a Rational.
⸺ Ruby docs

So this behavoir is kinda but ambiguously defined. I see you have decided to reflect it in your patch.

[ParadoxV5]

Tested and confirmed, Kernel#Rational indeed can return non-Rationals, like how the RBS describes. Smells more a Ruby bug than a feature.

[ParadoxV5]

With exception: false already covered, can this simply be

Suggested change

	| (_ToInt | _ToR numer, ?_ToInt | _ToR denom, ?exception: bool) -> Rational
	| (_ToInt | _ToR numer, ?_ToInt | _ToR denom, ?exception: true) -> Rational

?

Also applies to other conversion methods in Kernel.
Does not apply to the [T] ones if they don’t squelch exceptions as you said.

BTW,

Rational 1, 0, exception: false #=! ZeroDivisionError: divided by 0

[sampersand]

the : false case is for when a typechecker can explicitly determine that it's falsey. the : bool variant is when the typechecker doesn't have enough information.

[sampersand]

It might make sense to "default" to having Rational? be the default

[ParadoxV5]

the : false case is for when a typechecker can explicitly determine that it's falsey. the : bool variant is when the typechecker doesn't have enough information.

Not falsey, just false. Ruby rejects exception: nil. It also rejects boolishes, only accepting true.

[ParadoxV5]

Could there be a world where bool has three values? 💭

[sampersand]

Consolidated in #1445