Set<T>

Set stores distinct values. Uniqueness is determined jointly by the language's built-in equality and hash rules; Equatable and Hashable do not replace those rules.

Set<String> permissions = Set<>()
permissions.add("orders.read")

Boolean allowed = permissions.contains("orders.read")

add reports whether a new element was inserted; remove reports whether an element was found and removed. Value elements are deduplicated structurally, while class elements use object identity.

Set operations

Set<String> all = left.union(right)
Set<String> common = left.intersection(right)
Set<String> onlyLeft = left.difference(right)

These operations return new sets without modifying their inputs. Any in-place mutable variants must have distinct names.

Order and copying

A general Set does not guarantee iteration order. Set itself is a value; a copy has independent set structure, while class elements within it retain object identity.