delphi - 为什么缺少可选参数会导致 "Incompatible types"错误

Question

有人可以解释一下为什么当我省略构造函数的可选参数时，在以下程序中出现“不兼容类型”错误(Delphi XE3)(有关详细信息，请参阅代码底部的注释)？

program Test;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  System.Classes;

type
  BaseClass = class(TObject);

  ChildClass = class(BaseClass);

  GenericBaseClass<T> = class
  public
    constructor Create(Fixed: Integer);
  end;

  GenericClass<T: BaseClass> = class(GenericBaseClass<T>)
  public
    type
      TMyProc = procedure (DataObject: T) of object;
  public
    constructor Create(Fixed: String; Optional: TMyProc = nil);
  end;

constructor GenericClass<T>.Create(Fixed: String; Optional: TMyProc);
begin
  inherited Create(12);
end;

constructor GenericBaseClass<T>.Create(Fixed: Integer);
begin
  inherited Create();
end;

var
  Gc: GenericClass<ChildClass>;

begin
  // this call is okay
  Gc := GenericClass<ChildClass>.Create('', nil);
  // this call fails: E2010 Incompatible types: 'ChildClass' and 'T'
  Gc := GenericClass<ChildClass>.Create('');
end.

Answer 1

将 reintroduce 或 overload 添加到 GenericClass 构造函数，因为您有多个具有相同名称但参数不同的构造函数。