Golang proposal: iter: Enumerate, Keys and Values functions

Proposal Details

I think it's will be common to work with iter.Seq and iter.Seq2 simultaneously, but there is no quick way to go from iter.Seq to iter.Seq2 and vice versa, so I propose to add new functions for iter package

func Enumerate[T any](it iter.Seq[T]) iter.Seq2[int, T] {
    return func(yield func(int, T) bool) {
        i := 0
        for v := range it {
            if !yield(i, v) {
                return
            }
            i++
        }
    }
}

func Keys[T1, T2 any](it iter.Seq2[T1, T2]) iter.Seq[T1] {
    return func(yield func(T1) bool) {
        for k := range it {
            if !yield(k) {
                return
            }
        }
    }
}

func Values[T1, T2 any](it iter.Seq2[T1, T2]) iter.Seq[T2] {
    return func(yield func(T2) bool) {
        for _, v := range it {
            if !yield(v) {
                return
            }
        }
    }
}

Comment From: gabyhelp

Related Issues and Documentation

• proposal: iter: convert between Seq and Seq2 #67334
• proposal: Go 2: range-over-function + range over types implementing iterator interface #65742 (closed)
• iter: new package for iterators #61897 (closed)
• proposal: Go 2: iterators #40605 (closed)

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Comment From: mymmrac

Proposal #67334 introduces more flexible, but complex ways to handle this issue Proposal #61898 doesn't touch on issue of going from iter.Seq to iter.Seq2 and vice versa

Comment From: jimmyfrasche

The top level comment of #61898 does not touch on but these all have come up in the discussion (along with their generalizations).

Comment From: mymmrac

I found a comment about those functions, and the explanations seem reasonable, so I guess this is just a duplicate issue, closing it