Go Maps

Internal

• Go Built-in Types

Overview

A map is an unordered collection of key-value pairs.

Declaration

Long Declaration

var map_identifier map[key_type]value_type

Example of a map of string to ints:

var m map[string]int

Note that maps must be initialized before attempting to write into them, see Assinging a Value to an Unitialized Map.

Declaration and initialization:

var m map[string]string = make(map[string]string)

Short Declaration

m := make(map[string]string)

Map Operators and Functions

Indexing Operator

Indexing operator [] returns the value corresponding to the specified key. If the key does not exist, the zero value for the value type is returned.

Assigning a Value to an Uninitialized Map

If the indexing operator is also used to assign a value to a key for an uninitialized map, we get a runtime error:

panic: assignment to entry in nil map

Map Length

len() returns the number of keys.