Maps

m := make(map[string]int)

// set the value
m["three"] = 3
m["four"] = 4

// get the value and see if the value exists
key := "four"
if value, ok := m[key]; ok {
	fmt.Printf("Key '%s' exists and maps to %d\n", key, value)
} else {
	fmt.Printf("Key '%s' doesn't exists\n", key)
}

key = "five"
if value, ok := m[key]; ok {
	fmt.Printf("Key '%s' exists and maps to %d\n", key, value)
} else {
	fmt.Printf("Key '%s' doesn't exists\n", key)
}

// if value doesn't exist, the result of lookup is zero value. In this case zero value of int is 0
fmt.Printf("\nValue for non-existing key: %d\n\n", m["not-exists"])

// iterating over keys and values
fmt.Printf("All keys and their values:\n")
for key, value := range m {
	fmt.Printf("%s => %d\n", key, value)
}

fmt.Printf("\nBefore deletion: len(m)=%d\n", len(m))
delete(m, "four")
fmt.Printf("After deletion : len(m)=%d\n", len(m))