3 ways to find a key in a map

Basics

When you index a map in Go you get two return values; the second one (which is optional) is a boolean that indicates if the key exists.

If the key doesn’t exist, the first value will be the default zero value.

Check second return value

m := map[string]float64{"pi": 3.14}
v, found := m["pi"] // v == 3.14  found == true
v, found = m["pie"] // v == 0.0   found == false
_, found = m["pi"]  // found == true

Use second return value directly in an if statement

m := map[string]float64{"pi": 3.14}
if v, found := m["pi"]; found {
	fmt.Println(v)
}
// Output: 3.14

Check for zero value

m := map[string]float64{"pi": 3.14}

v := m["pi"] // v == 3.14
v = m["pie"] // v == 0.0 (zero value)

Warning: This approach doesn't work if the zero value is a possible key.

Further reading

Maps explained [code example]

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