Set (abstract Data Type) - Language Support

Language Support

One of the earliest languages to support sets was Pascal; many languages now include it, whether in the core language or in a standard library.

• Java offers the Set interface to support sets (with the HashSet class implementing it using a hash table), and the SortedSet sub-interface to support sorted sets (with the TreeSet class implementing it using a binary search tree).
• Apple's Foundation framework (part of Cocoa) provides the Objective-C classes NSSet, NSMutableSet, NSCountedSet, NSOrderedSet, and NSMutableOrderedSet. The CoreFoundation APIs provide the CFSet and CFMutableSet types for use in C.
• Python has built-in set and frozenset types since 2.4, and since Python 3.0 and 2.7, supports non-empty set literals using a curly-bracket syntax, e.g.: {x, y, z}.
• The .NET Framework provides the generic HashSet and SortedSet classes that implement the generic ISet interface.
• Smalltalk's class library includes Set and IdentitySet, using equality and identity for inclusion test respectively. Many dialects provide variations for compressed storage (NumberSet, CharacterSet), for ordering (OrderedSet, SortedSet, etc.) or for weak references (WeakIdentitySet).
• Ruby's standard library includes a set module which contains Set and SortedSet classes that implement sets using hash tables, the latter allowing iteration in sorted order.
• OCaml's standard library contains a Set module, which implements a functional set data structure using binary search trees.
• The GHC implementation of Haskell provides a Data.Set module, which implements a functional set data structure using binary search trees.
• The Tcl Tcllib package provides a set module which implements a set data structure based upon TCL lists.

As noted in the previous section, in languages which do not directly support sets but do support associative arrays, sets can be emulated using associative arrays, by using the elements as keys, and using a dummy value as the values, which are ignored.