Why is there Range and ClosedRange? Why RotatedShape?

[wowbagger (冀卓疌)]

@Hacksaw

I don't even know why they are different

Somewhat relevant (not specifically why Range and ClosedRange are different, but why there are different "range" types):

@beccadax

1. The current design enforces the correctness of iteration.

For instance, suppose you try to do this:

let myRange = ..<3
for i in myRange { ... }

This iteration is impossible to perform because it has no starting value—the last value will be 3, but what will the first value be? Fortunately, the compiler knows that it can’t iterate over a PartialRangeTo , so it rejects this code.

@beccadax

2. The current design makes loops over ranges much faster.

For instance, currently when the compiler sees this:

for i in myRange { ... }

It knows that it can turn that into something like:

var i = myRange.lowerBound
while i < myRange.upperBound {
  ...
  i &+= 1
}

And in general, it actually does—a Swift for i in someRange loop is nearly always as fast as a C for loop.