Go Maps

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Revision as of 23:43, 26 August 2024 by Ovidiu (talk | contribs) (→‎len())
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External

Internal

Overview

Maps and Pass-by-Value

Pointers to Maps

nil and Empty Map

nil Map

Empty Map

Declaration and Initialization

Initialization with make()

Initialization with a Composite Literal

Composite literals can be used for map initialization.

Long variable declaration and initialization with type inference:

var mm = map[string]int{"A": 1, "B": 2}

Short variable declaration:

mm := map[string]int{"A": 1, "B": 2}

Operators

Indexing Operator []

Values stored in a map can be referenced with the indexing operator [], using the [<key>] syntax. The indexing operator returns two values: the value associated with the key, if any, and a boolean that says whether the key exists or not in the map.

mm := map[string]int{"A": 1, "B": 2}
v, ok := mm["A"]
fmt.Printf("%d, %t\n", v, ok) // will display 1, true

If the key does not exist in map, the retuned value is not nil, but the zero value for the type.

The indexing operator can be used to change the value associated with a key, or to add a new key/value pair:

mm["A"] = 7
mm["C"] = 9

Map Functions

delete()

len()

len() returns the number of keys. Note that the built-in cap() function does not work on maps. Unlike slices, maps do not have the concept of capacity.

make()

new()

Iterating over a Map

TODO

Go_Maps_TODEPLETE