This is analogous to a ternary conditional operator, but it evaluates its consequent and alternative values eagerly, which makes it less useful. However, I understand that we're not likely to see such an operator in Go any time soon.

I'll note that it should be

func Cond[T any, B ~bool](cond B, ifval, elseval T) T

I mean, you can make it lazy if you want: https://go.dev/play/p/D9BDFlGF-Uf

I'll note that it should be

func Cond[T any, B ~bool](cond B, ifval, elseval T) T

I don't think it's worthwhile to make it generic over bool types. If it were builtin, sure.

Of course, if it were builtin, it should be lazy.

I disagree. bool is a declared type and it would be pretty frustrating, having to convert it if you happen to use a user-declared boolean type (this is different for slices, for example, where type MySlice []T is assignable to []T). Not that declaring boolean types is incredibly common, but it's not unheard of. And the cost seems close to zero. For a standard library function, it seems like a no-brainer to me, that we'd want to make it as general as we can.

I mean, you can make it lazy if you want: https://go.dev/play/p/D9BDFlGF-Uf

That is impressive extends to go through to not write a simpler if check.

#36303 proposal: new builtin to pick from one of two values

#37739 proposal: Go 2: lazy values

Zig's solution:

_ = if (cond) ifval else elseval;

Python's solution:

_ = ifval if cond else elseval

Skips () but is not intuitive (it's forced by parser limitations and falls out of the requirements but it's still weird).

Of course, if it were builtin, it should be lazy.

👎 this would be weird magic, currently builtins only cheat about the type system (generics before we had generics and ~string → ~[]byte signature overload) but not control flow. The value of adding control flow cheats so you can save a couple of ⏎ presses is low to me.

I had not seen #36303 before. Looks like the builtin version of this has been rejected. I still think the cmp.Cond version is marginally convenient and fits with the general vibe of package cmp.