How to concatenate two Go 1.23 iter.Seq[E] together?

Question

Go 1.23 comes with the new iter package and range-over-func feature.

Given two iterators, what's the correct way to combine them together?

import "slices"

func main() {
    a := []int{1, 2, 3, 4}
    b := []int{5, 6, 7, 8}

    i := slices.Values(a) // i is iter.Seq[int]
    j := slices.Values(b) // j is iter.Seq[int]

    // ???
}

The goal here is to iterate over both slices' elements in order, from 1 to 8. Apparently there isn't any ready-made helper in the slices package, is there?

Answer 1

True, the iter package provides no function for concatenating two iter.Seq[E], but you can implement one easily enough. Below is a Concat function (borrowed from my jub0bs/iterutil package) that takes a variadic parameter:

package main

import (
    "fmt"
    "iter"
    "slices"
)

// borrowed from https://pkg.go.dev/github.com/jub0bs/iterutil#Concat
func Concat[E any](seqs ...iter.Seq[E]) iter.Seq[E] {
    return func(yield func(E) bool) {
        for _, seq := range seqs {
            for e := range seq {
                if !yield(e) {
                    return
                }
            }
        }
    }
}

func main() {
    a := []int{1, 2, 3, 4}
    b := []int{5, 6, 7, 8}

    for i := range Concat(slices.Values(a), slices.Values(b)) {
        fmt.Print(i, ",")
    }
}

Output:

1,2,3,4,5,6,7,8,

(Playground)