Delphi 中的泛型类型指针

lymgl2op  于 2023-04-11  发布在  其他
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在 Delphi 中是否可以创建泛型类操作符或泛型指针?

AppleList[1].Color:=9999;
writeln(AppleList[1].Color); //Expected result is 9999

目标是这个或类似的,但有一个语法错误:

IList<T>=interface
   function GetItem(const aIndex:integer):T; 
   function GetRef(const aIndex:integer):^T; //!!!!Syntax ERROR
   property Items[const aIndex:integer]:T read GetItem;
   property RefItems[const aIndex:integer]:^T read GetRef; //!!!!Syntax ERROR
end;

TList<T>=class(TInterfacedObject,IList<T>)
   function GetItem(const aIndex:integer):T;
   function GetRef(const aIndex:integer):^T;
   ...
   property Items[const aIndex:integer]:T read GetItem;
   property RefItems[const aIndex:integer]:^T read GetRef;default;
   class operator Implicit(a:T):^T;
end;

TApple=record //or class
  Size:double;
  Color:integer;
end;

begin
  var AppleList:IList<TApple>;
  AppleList:=TList<TApple>.Create;
  var apple:TApple;
  apple.Color:=10;
  AppleList.Add(apple);
  AppleList.Items[1].Color:=9999;
  writeln(AppleList[1].Color); //result is 10 instead of 9999 //NOT WORKS!!!!

  AppleList.RefItems[1].Color:=2;
  writeln(AppleList.RefItems[1].Color); //result:2 //It WORKS

  AppleList[1].Color:=3;
  writeln(AppleList[1].Color); //result:3 //It WORKS
  //AppleList:=nil; no need! it is interface!
end.
zsbz8rwp

zsbz8rwp1#

记录是通过值传递的,而不是通过引用传递的。这就是为什么你会得到错误的输出。将TApple更改为Tobject的类。然后通过调用AppleList.Items[1],你会得到一个对苹果的引用,其中的Color值会被更改。

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