Data Structures, Containers, Collections

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Most programs operate on data, either searching, sorting, iterating or simply insert and retrieve. Therefore, a means of data structure, containers and collections is required.

Free Pascal ships with numerous data structures, at different levels (RTL, FCL) but there are also third party solutions offering such feature.


  • Classes unit
    • TList: Manages a list of pointers, can search and sort the list, has event notification feature
    • TFPList: Manages a list of pointers, can search and sort the list, without event notification feature, faster than TList
    • TStrings: Manages a list of strings, can search, split, save to / load from file, store objects, act like associative array, etc., is an abstract class
    • TStringList: TStrings descendant, implements abstract methods of TStrings, can sort, handle duplicates, has event notification feature, a concrete class
    • TBits: Manages a list of bits (0 or 1), useful for bit-map (not bitmap image format)
    • TCollection and TCollectionItem: Forms basic management of named items
  • FGL (Free Generics Library) unit
    • TFPGList
    • TFPGObjectList
    • TFPGInterfacedObjectList
    • TFPGMap
    • TFPGMapInterfacedObjectData



  • AVL_Tree unit
    • TAVLTree and TAVLTreeNode
  • Contnrs unit
    • TFPObjectList
    • TObjectList
    • TComponentList
    • TClassList
    • TOrderedList
    • TStack
    • TObjectStack
    • TQueue
    • TObjectQueue
    • TFPHashList
    • TFPHashObjectList
    • TFPDataHashTable
    • TFPStringHashTable
    • TFPObjectHashTable
    • TBucketList
    • TObjectBucketList


  • GVector unit
    • TVector: Implements dynamically self-resizing array, item order is based on insertion order
  • GSet unit
    • TSet: Implements red-black tree backed set, no order is guaranteed
  • GHashSet unit
    • THashSet: Implements hashtable backed set, no order is guaranteed
  • GStack unit
    • TStack: Implements stack, LIFO (last in first out) order
  • GQueue unit
    • TQueue: Implements stack, items are pushed from front, FIFO (first in first out) order
  • GPriorityQueue unit
    • TPriorityQueue: Implements heap backed priority queue, order is based on given compare function
  • GDeQue unit
    • TDeque: Implements double ended queue, items can be pushed and popped from either front or back
  • GMap unit
    • TMap: Implements TSet (and therefore, red-black tree) backed map
  • GHashMap unit
    • THashMap: Implements hashtable backed map
  • GTree unit
    • TTree: Implements k-ary tree, supports depth first and breadth first traversal

3rd party