cmd/compile: compiler permits variadic yield functions for range-over-func

[griesemer]

The compiler accepts (playground)

package main

import "fmt"

func main() {
	for a := range f {
		fmt.Println(a)
	}
}

func f(yield func(...int) bool) {
	yield(1)
	yield(1, 2)
	yield(1, 2, 3)
}

yet the spec does not explicitly allow this.

It is also confusing because the type of the yield function argument (...int in this case) does not match the type of the iterator variable ([]int in this case).

[rothelius]

Another argument against: a func(func(...int) bool) is not assignable to an iter.Seq[T] for any type T.

[gopherbot]

Change https://go.dev/cl/761682 mentions this issue: go/types, types2: in range-over-func, the yield function cannot be variadic

[gopherbot]

Change https://go.dev/cl/761701 mentions this issue: spec: in range-over-func, the yield function cannot be variadic

[gabyhelp]

Related Issues

• range over func: it is NOT yet permitted to omit unwanted variables #67075 (closed)
• spec: for-range iterator yield function requires bool result - consider generalizing to any boolean type #71164
• spec: allow range-over-func to omit iteration variables #65236 (closed)
• spec: add range over int, range over func #61405 (closed)
• cmd/compile: compiler accepts range over int for any language version #64704 (closed)
• iter: range over seq (variable of type iter.Seq[T]) must have one iteration variable #64645 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}