Golang Maps

In the Go programming language there are maps, these have nothing to do with real world maps.

Maps in Golang associates a value to a key, you can see this as a table or set with pairs. A value can be retrieved using the key. This idea comes from hash map in computer science.

In a (hash) map, there are pairs of (key,values). For every value, there is one key. You can map a string to an int like this:

var m = make(map[string]int)

This create a map (string -> int) and initialises it.

Example

In this example we define a mapping of string to int. Then we create one pair and output it.

package main

import (
    "fmt"
)

func main() {
    var m = make(map[string]int)
    m["Apple"] = 1
    fmt.Println(m["Apple"])
}

The program outputs

$ go run example.go
1

You can define multiple key,value mappings in your map.

    m["Apple"] = 1
    m["Berry"] = 2
    m["Cherry"] = 3

If you want to iterate over the entire map, you can use this for loop:

for key, value := range m {
    fmt.Println("Key:", key, "Value:", value)
}

Other mappings

A map can also be a set of int to string pairs.

var m = make(map[int]string)

In the example below we use that for months:

package main

import (
    "fmt"
)

func main() {
    var m = make(map[int]string)
    m[1] = "January"
    m[2] = "February"
    m[3] = "March"
    for key, value := range m {
        fmt.Println("Key:", key, "Value:", value)
    }
}

You can also map int to int, consider this example:

var m = make(map[int]int)
m[1] = 1359
m[2] = 4639       
m[3] = 1234

Related links:

• More maps examples
• Learn Go