`...` vs `..=` for inclusive ranges

internals ideas (deprecated)
103

how about

for 5 < i <= 10
for 5<= i < 10

or the other way around

for 10 > i >= 0
for 10 >= i > 0

and so on?

104

I like this but it’s ambiguous outside a for loop. How would you declare a range?

let range = 5 < i <= 10; // what is i for?
for item in range { ... }
for item in (10 > i > 0) { ... } // what is i?

perhaps

for item in (10 > _ > 0) { ... }

would do?

1 Like
105

Well I like the idea for ranges

let range2 = 10  > .. >= 6

so

let range1 = 5 <= .. < 16

is desugar for

let range1 = 5..16

but I still think that this separation in for is nice

for 10 > idx > 0 { ... }

is clear as water, even

for idx in 10 > .. > 0 { ...}

than instead (which doesnt work right now)

for idx in 9..-1 {
}

you need to write some like

let r1 = 1..10;
for idx in r1.rev() {
    println!("{:?}", idx);
}
106

It'd work in C++ (overload operator <=(FullRange, T) to return RangeToInclusive<T>), but PartialOrd says <= can only return bool, via partial_cmp returning Option<Ordering>, so I assume it can't work in Rust. (And PartialOrd requires PartialEq, so it'd also allow silliness like 4 == .. == 2.) I assume it'd be completely doable as a macro, though. Then you could even make range!(0 <= r) turn RangeTo(5) into Range(0, 5).

Let me also plug the comment I posted on the other thread about ranges. TL/DR: From an algorithmic perspective, I think all std should provide is the Range [a,b) where b is 'reachable' from a by zero-or-more-but-finite applications of a successor function (aka, roughly, a ≤ b). Going beyond that feels like we're making an interval library, which is a totally different thing, and the current range is no better than a pair.

107

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