Question

可能重复：
Generic method returning generic interface in Delphi 2010

在Delphi 2010中，何时ISomeGenericInterface<T>可分配给ISomeGenericInterface<T>？

以下程序按预期编译并运行......

unit uGenDemo;
interface

{.$define declare-a-type}

function Tokenize: IEnumerator<string>;
{$IFDEF declare-a-type}
type TX = integer;
{$ENDIF}

implementation  

uses SysUtils;

type
IStringEnumerator = interface( IEnumerator<string>)
    ['{3A28E4FB-CDF7-4933-8D67-D9EF5C2466E0}']
  end;

TBaseEnumerator = class( TInterfacedObject, IEnumerator)
  private
    function  MoveNext: Boolean;
    function  BaseGetCurrent: TObject;
    function  IEnumerator.GetCurrent = BaseGetCurrent;
    procedure Reset;
  end;

TStringEnumerator = class( TBaseEnumerator, IStringEnumerator)
  private
    function GetCurrent: string;
    property Current: string read GetCurrent;
  end;

function Tokenize: IEnumerator<string>;
begin
result := TStringEnumerator.Create as IStringEnumerator
end;


{ TBaseEnumerator }

function TBaseEnumerator.BaseGetCurrent: TObject;
begin
result := nil
end;

function TBaseEnumerator.MoveNext: Boolean;
begin
result := False
end;

procedure TBaseEnumerator.Reset;
begin
end;

{ TStringEnumerator }

function TStringEnumerator.GetCurrent: string;
begin
result := ''
end;


end.

...但是当我们在声明Tokenize()函数后声明任何类型时，例如，通过更改...的行

{.$define declare-a-type}

...到......

{$define declare-a-type}

...编译器阻止并抛出错误......

[DCC Error] uGenDemo.pas(43): E2010 Incompatible types: 'IEnumerator<System.string>' and 'IStringEnumerator'

为什么吗

这是编译错误吗？
一般来说，将接口指针分配给一般参数化的祖先类型的接口指针是否安全？

（我的编译器版本是Embarcadero®Delphi®2010版本14.0.3593.25826）

何时ISomeGenericInterface <t>可分配给ISomeGenericInterface <t>？</t> </t>

0 个答案: