2.2 KiB
Map
Map is a mutable collection of key-value pars, where keys are unique. Maps could be created with
constructor or .toMap methods. When constructing from a list, each list item must be a [Collection] with exactly 2 elements, for example, a [List].
Constructed map instance is of class Map and implements Collection (and therefore Iterable)
val map = Map( ["foo", 1], ["bar", "buzz"] )
assert(map is Map)
assert(map.size == 2)
assert(map is Iterable)
>>> void
Map keys could be any objects (hashable, e.g. with reasonable hashCode, most of standard types are). You can access elements with indexing operator:
val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
assert( map["bar"] == "buzz")
assert( map[42] == "answer" )
assertThrows { map["nonexistent"] }
assert( map.getOrNull(101) == null )
assert( map.getOrPut(911) { "nine-eleven" } == "nine-eleven" )
// now 91 entry is set:
assert( map[911] == "nine-eleven" )
map["foo"] = -1
assert( map["foo"] == -1)
>>> void
To remove item from the collection. use remove. It returns last removed item or null. Be careful if you
hold nulls in the map - this is not a recommended practice when using remove returned value. clear()
removes all.
val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
assertEquals( 1, map.remove("foo") )
assert( map.getOrNull("foo") == null)
assert( map.size == 2 )
map.clear()
assert( map.size == 0 )
>>> void
Map implements [contains] method that checks the presence of the key in the map:
val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
assert( "foo" in map )
assert( "answer" !in map )
>>> void
To iterate maps it is convenient to use keys method that returns [Set] of keys (keys are unique:
val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
for( k in map.keys ) println(map[k])
>>> 1
>>> buzz
>>> answer
>>> void
It is possible also to get values as [List] (values are not unique):
val map = Map( ["foo", 1], ["bar", "buzz"], [42, "answer"] )
assertEquals(map.values, [1, "buzz", "answer"] )
>>> void