Collections

Kelvra currently ships built-in arrays, sets, and dictionaries. The tests under tests/ are the best source of truth for current behavior.

Arrays

Array literals use square brackets.

var values Array<i32> = [1, 2, 3]
print(values[0])

values[1] = 9
values[0] += 4

values.push(7)
print(values.pop())
print(values.size())
print(values.has(3))

Array methods are push, pop, insert, remove, clear, size, isEmpty, first, last, and has. Indexed reads, indexed writes, and compound assignment on indexed elements are also supported.

Sets

Sets support constructor-style creation and membership operations.

var ids Set<i32> = Set(1, 2, 2, 3)
print(ids.size())
print(ids.has(2))

print(ids.add(4))
print(ids.remove(3))

var more Set<i32> = Set(3, 4, 5)
print(ids.union(more))
print(ids.intersect(more))
print(ids.difference(more))

Set methods are add, remove, has, clear, isEmpty, size, toArray, union, intersect, and difference. Set values can be iterated directly:

for (var item i32 : ids) {
  print(item)
}

Dictionaries

Dictionaries use key/value literals with braces.

var scores Dict<str, i32> = {"alice": 7, "bob": 9}
print(scores["alice"])

scores["alice"] = 8
print(scores.get("alice"))

scores.set("carol", 10)
print(scores.has("carol"))
print(scores.size())
print(scores.remove("carol"))

Dictionary methods are get, getOr, set, has, remove, clear, isEmpty, size, keys, and values. Bracket access reads and writes values. Direct foreach over a dictionary is rejected today; iterate a projection such as .keys() instead.

Generic types

Collections are parameterized with angle-bracket type arguments:

var nums Array<i32> = []
var seen Set<str> = Set()
var players Dict<usize, i32> = Dict()

The codebase also uses nested collection types such as Dict<Array<i32>, i32>.

Collection literals and inference

Local inference works well when the target type is already clear:

var nums Array<i32> = [1, 2, 3]
var empty Set<str> = Set()
var mapping Dict<str, i32> = {}

When the literal alone is ambiguous, keep the explicit collection type.

Iteration patterns

var nums Array<i32> = [1, 2, 3]
for (var n i32 : nums) {
  print(n)
}

var scores Dict<str, i32> = {"alice": 7, "bob": 9}
for (var name str : scores.keys()) {
  print(scores[name])
}