Golang: Map

By Xah Lee. Date: . Last updated: .

Map is a unordered collection of key value pairs. Similar to dictionary, hashtable, associative array, in other languages.

Each key value pair is called an element.

Syntax of Map Type

Syntax of the map type is:

map[key_type_name]value_type_name

package main

import "fmt"
import "reflect"

func main() {

    // syntax of map type
    var mm map[string]int

    fmt.Println(reflect.TypeOf(mm)) // map[string]int
}

Create Map, Literal Expression

package main

import "fmt"

func main() {

    var mm = map[string]int{"a": 1, "b": 2}

    fmt.Println(mm) // map[a:1 b:2]
}

Create Map with make

package main

import "fmt"

func main() {

    var mp = make(map[string]int)

    mp["a"] = 1
    mp["b"] = 2

    fmt.Println(mp) // map[a:1 b:2]
}

set value, add key

m[k] = v → sets value v to key k in map m.

package main

import "fmt"

func main() {

    var mm = map[string]int{"a": 1, "b": 2}

    // set value to existing key
        mm["a"] = 9
    fmt.Println(mm) // map[a:9 b:2]

    // if key don't exist, add it
        mm["c"] = 8
    fmt.Println(mm) // map[a:9 b:2 c:8]

}

get value

m[k] → returns 2 values. First value is the value of key k in map m. Second value is true if the key exist, else false.

When a key does not exist, the first value is the “zero value”.

[see Zero Value]

package main

import "fmt"

func main() {

    var mm = map[string]int{"a": 1, "b": 2}

    // get
    var x = mm["a"]
    fmt.Println(x) // 1

    // returns 2 values. second is true if exist, else false
    var y, z = mm["b"]
    fmt.Println(y, z) // 2 true

    // returns 2 values. second is true if exist, else false
    var h1, h2 = mm["c"]
    fmt.Println(h1, h2) // 0 false

}

delete key

delete(m, k) → delete the key k in m. if key doesn't exist, do nothing.

package main

import "fmt"

func main() {

    var mm = map[string]int{"a": 1, "b": 2}

    // delete a key
        delete(mm, "a")
    fmt.Println(mm) // map[b:2]

    // if key doesn't exist, do nothing
        delete(mm, "9")
    fmt.Println(mm) // map[b:2]

}

Loop Thru Map

Golang: loop

Reference

The Go Programming Language Specification - The Go Programming Language#Map_types

The Go Programming Language Specification - The Go Programming Language#Deletion_of_map_elements

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Golang

  1. Compile, Run
  2. Source Encoding
  3. Package, Import
  4. Comment
  5. Print
  6. String
  7. Rune
  8. String as Chars
  9. Variable
  10. Zero Value
  11. Constant
  12. If Then Else
  13. Switch/Case
  14. Loop
  15. Basic Types
  16. Array
  17. Slice
  18. Map
  19. Struct
  20. Function
  21. regexp
  22. Read File
  23. Write to File
  24. Walk Dir
  25. Check File Exist
  26. System Call
  27. Get Script Path
  28. Pointer
  29. Defer
  30. Random Number

Examples

  1. match any regexp
  2. Validate Links
  3. Generate Sitemap

Reference

  1. Go Spec