Difference between revisions of "Generics"
m (Text replace - "delphi>" to "syntaxhighlight>") |
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Generic class is defined using keyword '''generic''' before class name and use in class declaration: | Generic class is defined using keyword '''generic''' before class name and use in class declaration: | ||
| − | < | + | <syntaxhighlight>type |
generic TList<T> = class | generic TList<T> = class | ||
Items: array of T; | Items: array of T; | ||
procedure Add(Value: T); | procedure Add(Value: T); | ||
| − | end;</ | + | end;</syntaxhighlight> |
Example of generic class implementation: | Example of generic class implementation: | ||
| − | < | + | <syntaxhighlight>implementation |
procedure TList.Add(Value: T); | procedure TList.Add(Value: T); | ||
| Line 19: | Line 19: | ||
SetLength(Items, Length(Items) + 1); | SetLength(Items, Length(Items) + 1); | ||
Items[Length(Items) - 1] := Value; | Items[Length(Items) - 1] := Value; | ||
| − | end;</ | + | end;</syntaxhighlight> |
Generic class can be simply specialized for particular type by use '''specialize''' keyword. | Generic class can be simply specialized for particular type by use '''specialize''' keyword. | ||
| − | < | + | <syntaxhighlight>Type |
TIntegerList = specialize TList<Integer>; | TIntegerList = specialize TList<Integer>; | ||
TPointerList = specialize TList<Pointer>; | TPointerList = specialize TList<Pointer>; | ||
| − | TStringList = specialize TList<string>;</ | + | TStringList = specialize TList<string>;</syntaxhighlight> |
==fgl unit== | ==fgl unit== | ||
Revision as of 15:22, 24 March 2012
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:
type
generic TList<T> = class
Items: array of T;
procedure Add(Value: T);
end;Example of generic class implementation:
implementation
procedure TList.Add(Value: T);
begin
SetLength(Items, Length(Items) + 1);
Items[Length(Items) - 1] := Value;
end;Generic class can be simply specialized for particular type by use specialize keyword.
Type
TIntegerList = specialize TList<Integer>;
TPointerList = specialize TList<Pointer>;
TStringList = specialize TList<string>;fgl unit
fgl unit is prototype unit for base system generic classes. So far it contains few basic classes:
- TFPGList
- TFPGObjectList
- TFPGInterfacedObjectList
- TFPGMap
Technical details
1. The compiler parses a generic, but instead of generating code it stores all tokens in a token buffer inside the PPU file.
2. The compiler parses a specialization; for this it loads the token buffer from the PPU file and parses that again, but replaces the generic parameters (in most examples "T") by the particular given type (e.g. LongInt, TObject). The code basically appears as if the same class had been written as the generic but with T replaced by the given type.
Therefore in theory there should be no speed differences between a "normal" class and a generic one.
