Maps #

Slow has a built-in map type that is implemented using a hash table constructed from Go’s map type. Map literals are declared using curly brackets:

var m = {}

Like lists, you can also specify elements in a map literal:

m = {1: 2, 3: 4, true: 1, "foo": "bar"}

Only hashable types may be used as map keys; the only types that are currently hashable are primitives. Any type may be used as a value in a map.

Maps can be either mutable or immutable; all maps are mutable by default, by an immutable copy of any map can be created with the to_immutable method described below. (Similarly, a mutable copy of any map can be created with the to_mutable method.) Immutable maps do not allow any modification (e.g. index assignment, map.set). However, making an immutable map does not make its elements themselves immutable.

Map Methods #

The map type has several built-in methods, each of which is described below.

map.get #

The get method of a map returns the value corresponding to the provided key.

var m = {1: 2}
m.get(1)
> 2

If the specified key is not in the map, a KeyError is thrown. You can specify a default value for a key by passing in a second value:

-> var m = {1: 2}
{1: 2}
-> m.get(1)
2
-> m.get(3, 4)
4

map.set #

The set method of a map creates a new key-value pair in the map. It returns true if the key was already present in the map (i.e. if it was overwritten) and false if it was not.

-> var m = {1: 2}
{1: 2}
-> m.set(3, 4)
false
-> m.set(1, 3)
true

The provided key must be of a hashable type.

map.to_mutable #

The to_mutable method of map creates a mutable copy of the map. This method can be used on any map (immutable or mutable).

-> var m1 = {1: 2}
{1: 2}
-> var m2 = m1.to_mutable()
{1: 2}
-> m2.set(3, 4)
-> m1
{1: 2}
-> m2
{1: 2, 3: 4}

map.to_immutable #

The to_immutable method of map creates an immutable copy of the map. This method can be used on any map (mutable or immutable).

-> var m1 = {1, 2}
{1: 2}
-> var m2 = m1.to_immutable()
{1: 2}
-> m1.set(3, 4)
false
-> m1
{1: 2, 3: 4}
-> m2.set(3, 4)
ValueError: map is immutable