Go: Check if a map contains a key

m := map[string]float64{"pi": 3.1416}

v1 := m["pi"]  // v1 == 3.1416
v2 := m["foo"] // v2 == 0.0 (zero value)

_, exists := m["pi"] // exists == true

if x, ok := m["pi"]; ok {
        fmt.Println(x) // 3.1416
}