Map
A map maps keys to values.
The zero value of a map is nil. A nil map has no keys, nor can keys be added.
The make function returns a map of the given type, initialized and ready for use.
package main
import "fmt"
type Vertex struct {
Lat, Long float64
}
var m map[string]Vertex
// m is type of map, key is type of string, value is type of Vertex
func main() {
m = make(map[string]Vertex)
m["Bell Labs"] = Vertex{
40.68433, -74.39967,
}
fmt.Println(m["Bell Labs"])
}
// {40.68433 -74.39967}
Map literals
Map literals are like struct literals, but the keys are required.
package main
import "fmt"
type Vertex struct {
Lat, Long float64
}
var m = map[string]Vertex{
"Bell Labs": Vertex{
40.68433, -74.39967,
},
"Google": Vertex{
37.42202, -122.08408,
},
}
func main() {
fmt.Println(m)
}
// map[Bell Labs:{40.68433 -74.39967} Google:{37.42202 -122.08408}]
If the top-level type is just a type name, you can omit it from the elements of the literal.
var m = map[string]Vertex{
"Bell Labs": {40.68433, -74.39967},
"Google": {37.42202, -122.08408},
}
Mutating Maps
Insert or update an element in map m:
m[key] = elem
Retrieve an element:
elem = m[key]
Delete an element:
delete(m, key)
Test that a key is present with a two-value assignment:
elem, ok = m[key]
// If elem or ok have not yet been declared you could use a short declaration form
elem, ok := m[key]
If key is in m, ok is true. If not, ok is false.