Generics

Introduction

Generics are native implementation of class templates. Generics are sometimes called parametrized types. FPC have official support for generics since version 2.2.

Examples

Generic class is defined using keyword generic before class name and use in class declaration: <delphi>type

 generic TList<T> = class
   Items: array of T;
   procedure Add(Value: T);
 end;</delphi>

Example of generic class implementation: <delphi>implementation

procedure TList.Add(Value: T); begin

 SetLength(Items, Length(Items) + 1);
 Items[Length(Items) - 1] := Value;

end;</delphi>

Generic class can be simply specialized for particular type by use specialize keyword. <delphi>Type

 TIntegerList = specialize TList<Integer>;
 TPointerList = specialize TList<Pointer>;
 TStringList = specialize TList<string>;</delphi>

fgl unit

fgl unit is prototype unit for base system generic classes. So faw it contains few basic classes:

• TFPGList
• TFPGObjectList
• TFPGInterfacedObjectList
• TFPGMap

See also

• Templates
• Generics proposals

External links

• Free Pascal: Reference guide - Generics