How to check if a map contains a key in Go

Use second return value directly in an if statement

If "BST" is indeed present in the map, the body of the if statement will be executed and v will be local to that scope.

package main

import "fmt"

func main() {

  dict := map[string]int{
    "UTC": 0 * 60 * 60,
    "BST": 1 * 60 * 60,
  }

  if _, ok := dict["UTC"]; ok {
    //do something here
    fmt.Println(dict["UTC"])
  }

}

3600

To test for presence in the map without worrying about the actual value, you can use the blank identifier (_) in place of the usual variable for the value.

Check second return value

if statements in Go can include both a condition and an initialization statement.

m := map[string]int{
  "foo": 1, 
  "bar": 2
}
v, ok := m["foo"] // v == 1  ok == true
v, ok = m["foooo"] // v == 0   ok == false
_, ok = m["foo"]  // ok == true

Check for zero value

if the map is nil or does not contain such an entry, a[x] is the zero value for the element type of M.

m := map[string]int{
  "foo": 1
}

v := m["foo"] // v == 1
v = m["fooooo"] // v == 0 (zero value)