Map
A collection that holds pairs of objects (keys and values) and supports efficiently retrieving the value corresponding to each key.
Literal for MutableMap is #{1 "one" 2 "two"} or #{1 "one", 2 "two"} because its hash based
Creating map
map = #{1 "one" 2 "two"}
// empty map is
map::MutableMap(Int, String) = #{}
Accessing elements
To get the element from the map you need to know its key. at: key message returns nullable value, in case there no such key, so you need to unpack it
map = #{1 "one" 2 "two"}
one = map at: 1
real = one unpackOrError
real = one unpackOrValue: "no value"
real = one unpack: [it echo]
You can iterate over keys and values with forEach message:
map forEach: [ k, v ->
"key: $k value: $v"
]
// or iterate over keys\values only
map values forEach: [it echo]
map keys forEach: [it echo]
Map also supports filter: and map: with the same signature as forEach:.
Check if there is a key or value:
map containsKey: 1
map containsValue: "2"
Mutation
x = #{1 "one"}
x at: 2 put: "two"
x remove: 1 // remove element by key
x clear // remove all elements
x putAll: #{2 "two" 3 "three"}
Common messages
map = #{1 "one"}
map isEmpty // false
The same as Sets, Maps support + and - messages, it creates new map, without mutation.
map1 = #{1 "one" 2 "two"}
map2 = #{1 "one"}
map3 = map1 - map2
>map1 //> {1=one, 2=two}
>map2 //> {1=one}
>map3 //> {1=one, 2=two}
It can be useful to construct a map based on a list with inject:into: message
//> {1=false, 2=true, 3=false, 4=true, 5=false}
>{3 4 5} inject: #{1 false 2 true} into: [map, cur ->
map at: cur put: cur % 2 == 0
map
]
Converting
You can take the values or set of keys from a map
map = #{1 "one" 2 "two"}
keys = map keys
values = map values
Last modified: 02 November 2024