Does Go have an iterator datatype?

How do I write Go code that can do something like a map iterator in C++?

typedef std::map<std::string, MyStruct> MyMap;
MyMap::iterator it = myMap.find("key");
if(it!=myMap.end()) {
   it->v1 = something;
   it->v2 = something;
}

In go, it is pretty easy to iterate over a map using the range clause.

myMap := map[string]int {"one":1, "two":2}

for key, value := range myMap {
  // Do something.
  fmt.Println(key, value)
}

Could print

one 1
two 2

Note that you iterate in an undefined order over a map, as it is backed by a hash table rather than a tree.

The go language spec describes what the range clause returns, and you can see the effective go page for some more examples.

If you're just trying to find a key in a map, then use the following:

package main

import (
    "fmt"
)

type Point struct {
    x, y int
}

func main() {
    points := make(map[string]*Point)

    p := &Point{1, 1}
    points["one"] = p

    if p1, found := points["one"]; found {
        p1.x = 100
    }

    fmt.Println(p)
}

For example,

package main

import "fmt"

type MyStruct struct {
	v1 string
	v2 int
}

type MyMap map[string]MyStruct

func main() {
	m := MyMap{
		"unum": MyStruct{"I", 1},
		"duo":  MyStruct{"II", 2},
	}
	fmt.Println("before:")
	for k, v := range m {
		fmt.Println(k, v)
	}
	var k string
	k = "unum"
	if v, ok := m[k]; ok {
		v.v1 = "one"
		v.v2 = 1
		m[k] = v
	}
	k = "tria"
	if v, ok := m[k]; ok {
		v.v1 = "III"
		v.v2 = 3
		m[k] = v
	}
	fmt.Println("after:")
	for k, v := range m {
		fmt.Println(k, v)
	}
}

Output:

before:
unum {I 1}
duo {II 2}
after:
unum {one 1}
duo {II 2}