Difference between revisions of "Generics"

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==Introduction==
 
==Introduction==
  
Generics are native implementation of class templates. Generics are sometimes called parametrized types. FPC have official support for generics since version 2.2.  
+
Generics are a native implementation of class templates. Generics are sometimes called parametrized types. FPC have official support for generics since version 2.2.  
  
 
==Examples==
 
==Examples==
  
Generic class is defined using keyword '''generic''' before class name and use in class declaration:
+
A generic class is defined using keyword '''generic''' before the class name and use in class declaration:
 
<syntaxhighlight>type
 
<syntaxhighlight>type
 
   generic TList<T> = class
 
   generic TList<T> = class
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==fgl unit==
 
==fgl unit==
  
fgl unit is prototype unit for base system generic classes. So far it contains few basic classes:
+
The fgl unit is a prototype unit for base system generic classes. So far it contains a few basic classes:
 
* TFPGList
 
* TFPGList
 
* TFPGObjectList
 
* TFPGObjectList
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== Technical details ==
 
== Technical details ==
  
1. The compiler parses a generic, but instead of generating code it stores  
+
1. The compiler parses a generic, but instead of generating code it stores all tokens in a token buffer inside the PPU file.
all tokens in a token buffer inside the PPU file.
 
  
2. The compiler parses a specialization; for this it loads the token buffer  
+
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).
from the PPU file and parses that again, but replaces the generic  
+
The code basically appears as if the same class had been written as the generic but with T replaced by the given type.
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.
 
Therefore in theory there should be no speed differences between a "normal" class and a generic one.

Revision as of 10:27, 7 June 2013

Introduction

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

Examples

A generic class is defined using keyword generic before the 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

The fgl unit is a prototype unit for base system generic classes. So far it contains a 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.

See also

External links