proposal: slices: add ForEach function to iterate

[agaraleas]

Proposal Details

Abstract
This proposal suggests adding a ForEach function to Go slices, inspired by the std::for_each function in C++. This function would simplify the iteration process over slices, providing a clear and concise way to apply a function to each element of a slice, enhancing readability and code organization.

Proposal
Add a function ForEach with a possible implementation like:

func ForEach[T any](s []T, f func(T)) {
    for _, v := range s {
        f(v)
    }
}

This function will allow users to apply a specified function to each element in a slice without the need for a for loop, improving a lot readability in situations like this example:

type BankAccount struct {
    Balance int
}

func printBalance(account *BankAccount) {
    fmt.Println(account.Balance)
}

func main() {
    accounts := []*BankAccount{{100}, {200}, {300}}
    slices.ForEach(accounts, printBalance)
}

A ForEach function lets us directly express the intent of the looping which in my opinion improves a lot readability and comprehension of a code, while being as concise as possible.

If community aggrees with the proposal, I would be happy to provide a PR with implementation.
Thank you

[seankhliao]

I believe in the general case this is Map, which would be part of iterators not slices, see #61898

[zigo101]

No, in the iterator age, the code should be like

package main

import "fmt"

func ForEach[T any](s []T, f func(T)) func(func() bool) {
	return func(yield func() bool) {
		for _, v := range s {
			f(v)
			if !yield() {
		    	return
		    }
		}
	}
}

type BankAccount struct {
    Balance int
}

func printBalance(account *BankAccount) {
    fmt.Println(account.Balance)
}

func main() {
    accounts := []*BankAccount{{100}, {200}, {300}}
    for range ForEach(accounts, printBalance) {}
}

:)

[zigo101]

Or even more graceful:

package main

import (
	"fmt"
	"slices"
)

func ForEach[E any](it func(func(V E) bool), f func(V E)) func(func() bool) {
	return func(yield func() bool) {
		for v := range it {
			f(v)
			if !yield() {
		    	return
		    }
		}
	}
}

type BankAccount struct {
    Balance int
}

func printBalance(account *BankAccount) {
    fmt.Println(account.Balance)
}

func main() {
    accounts := []*BankAccount{{100}, {200}, {300}}
    for range ForEach(slices.Values(accounts), printBalance) {}
}

[DeedleFake]

It's not Map(), as it doesn't return anything. It is, however, simply an unwieldy wrapper around just doing a for loop manually.

[agaraleas]

Thank you for your feedback.

• Why not include it in both iterators AND slices? Since slices is not deprecated and other functions will co-exist in both packages, I don't see why this one as well cannot be included in both as well.
• Doing a for manually does not express intention of the iteration. It just adds boilerlate code. To be honest, I believe this addition is the exact opposite of being unwieldy. And this is why something similar exists in most of other languages. It only improves readability by being concise giving the intention of the iteration in a single line