Is there a foreach loop in Go?

Is there a foreach construct in the Go language? Can I iterate over a slice or array using a for?

https://golang.org/ref/spec#For_range

> A "for" statement with a "range" clause iterates through all entries > of an array, slice, string or map, or values received on a channel. > For each entry it assigns iteration values to corresponding iteration > variables and then executes the block.

As an example:

for index, element := range someSlice {
	// index is the index where we are
	// element is the element from someSlice for where we are
}

If you don't care about the index, you can use _:

for _, element := range someSlice {
	// element is the element from someSlice for where we are
}

The underscore, _, is the blank identifier, an anonymous placeholder.

Go has a foreach-like syntax. It supports arrays/slices, maps and channels.

Iterate over an array or a slice:

// index and value
for i, v := range slice {}

// index only
for i := range slice {}

// value only
for _, v := range slice {}

Iterate over a map:

// key and value
for key, value := range theMap {}

// key only
for key := range theMap {}

// value only
for _, value := range theMap {}

Iterate over a channel:

for v := range theChan {}

Iterating over a channel is equivalent to receiving from a channel until it is closed:

for {
    v, ok := <-theChan
    if !ok {
        break
    }
}

Following is the example code for how to use foreach in golang

package main

import (
	"fmt"
)

func main() {
	
	arrayOne := [3]string{"Apple", "Mango", "Banana"}
	
	for index,element := range arrayOne{
	
		fmt.Println(index)
		fmt.Println(element)		
	
	}	
	
}

This is a running example https://play.golang.org/p/LXptmH4X_0

The following example shows how to use the range operator in a for loop to implement a foreach loop.

func PrintXml (out io.Writer, value interface{}) error {
    var data []byte
    var err error

    for _, action := range []func() {
        func () { data, err = xml.MarshalIndent(value, "", "  ") },
        func () { _, err = out.Write([]byte(xml.Header)) },
        func () { _, err = out.Write(data) },
        func () { _, err = out.Write([]byte("\n")) }} {
        action();
        if err != nil {
            return err
        }
    }
    return nil;
}

The example iterates over an array of functions to unify the error handling for the functions. A complete example is at Google´s playground.

PS: it shows also that hanging braces are a bad idea for the readability of code. Hint: the for condition ends just before the action() call. Obvious, isn't it?

You can in fact use range without referencing it's return values by using for range against your type:

arr := make([]uint8, 5)
i,j := 0,0
for range arr {
	fmt.Println("Array Loop",i)
	i++
}

for range "bytes" {
	fmt.Println("String Loop",j)
	j++
}

https://play.golang.org/p/XHrHLbJMEd

Yes, Range :

The range form of the for loop iterates over a slice or map.

When ranging over a slice, two values are returned for each iteration. The first is the index, and the second is a copy of the element at that index.

Example :

package main

import "fmt"

var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}

func main() {
	for i, v := range pow {
		fmt.Printf("2**%d = %d\n", i, v)
	}
	
	for i := range pow {
		pow[i] = 1 << uint(i) // == 2**i
	}
	for _, value := range pow {
		fmt.Printf("%d\n", value)
	}
}

• You can skip the index or value by assigning to _.
• If you only want the index, drop the , value entirely.

This may be obvious, but you can inline the array like so:

package main

import (
	"fmt"
)

func main() {
	for _, element := range [3]string{"a", "b", "c"} {
		fmt.Print(element)
	}
}

outputs:

abc

https://play.golang.org/p/gkKgF3y5nmt

I have jus implement this library:https://github.com/jose78/go-collection. This is an example about how to use the Foreach loop:

package main

import (
	"fmt"

	col "github.com/jose78/go-collection/collections"
)

type user struct {
	name string
	age  int
	id   int
}

func main() {
	newList := col.ListType{user{"Alvaro", 6, 1}, user{"Sofia", 3, 2}}
	newList = append(newList, user{"Mon", 0, 3})

	newList.Foreach(simpleLoop)
	
	if err := newList.Foreach(simpleLoopWithError); err != nil{
		fmt.Printf("This error >>> %v <<< was produced", err )	
	}
}

var simpleLoop col.FnForeachList = func(mapper interface{}, index int) {
	fmt.Printf("%d.- item:%v\n", index, mapper)
}


var simpleLoopWithError col.FnForeachList = func(mapper interface{}, index int) {
	if index > 1{
		panic(fmt.Sprintf("Error produced with index == %d\n", index))
	}
	fmt.Printf("%d.- item:%v\n", index, mapper)
}

The result of this execution should be:

0.- item:{Alvaro 6 1}
1.- item:{Sofia 3 2}
2.- item:{Mon 0 3}
0.- item:{Alvaro 6 1}
1.- item:{Sofia 3 2}
Recovered in f Error produced with index == 2

ERROR: Error produced with index == 2
This error >>> Error produced with index == 2
 <<< was produced

Try this code in playGrounD