将泛型与不同约束相结合

Question

我有这个原子乐观的初始化类:

type
  Atomic<T: IInterface> = class
    type TFactory = reference to function: T;
    class function Initialize(var storage: T; factory: TFactory): T;
  end;

class function Atomic<T>.Initialize(var storage: T; factory: TFactory): T;
var
  tmpIntf: T;
begin
  if not assigned(storage) then begin
    tmpIntf := factory();
    if InterlockedCompareExchangePointer(PPointer(@storage)^, PPointer(@tmpIntf)^, nil) = nil then
      PPointer(@tmpIntf)^ := nil;
  end;
  Result := storage;
end;

现在我想为对象实现相同的模式.

type
  Atomic<T: class> = class
    type TFactory = reference to function: T;
    class function Initialize(var storage: T; factory: TFactory): T;
  end;

class function Atomic<T>.Initialize(var storage: T; factory: TFactory): T;
var
  tmpIntf: T;
begin
  if not assigned(storage) then begin
    tmpIntf := factory();
    if InterlockedCompareExchangePointer(PPointer(@storage)^, PPointer(@tmpIntf)^, nil) = nil then
      tmpIntf.Free;
  end;
  Result := storage;
end;

我可以在两个单独的类中完成这两个,但我真的想把两个初始化器放在同一个伞下.我想,我最好还是喜欢这个

var
  o: TObject;
  i: IInterface;

Atomic<TObject>.Initialize(o, CreateObject);
Atomic<IInterface>.Initialize(i, CreateInterface);

我找不到任何好的解决方案.我得到的唯一想法是将类声明为Atomic<T>(没有约束)然后以某种方式(不知道如何)在运行时检查T的RTTI并相应地继续.

我不太喜欢这个想法,我正在寻找一个更好的方法.

Answer 1

看来您无法指定“类或接口”类型的约束。因此，最简单的解决方案似乎是放弃约束（您可以使用 RTTI 在运行时强制执行它）。

对于 RTTI 方法，您可以使用以下TypeInfo函数：

uses
  ..., TypInfo;    

class function Atomic<T>.Initialize(var storage: T; factory: TFactory): T;
var
  tmpT: T;
begin
  if not assigned(PPointer(@storage)^) then begin
    tmpT := factory();
    if InterlockedCompareExchangePointer(PPointer(@storage)^, PPointer(@tmpT)^, nil) = nil then begin
      case PTypeInfo(TypeInfo(T))^.Kind of
        tkInterface:
          PPointer(@tmpT)^ := nil;
        tkClass:
          TObject(tmpT).Free;
        else
          raise Exception.Create('Atomic<T>.Initialize: Unsupported type');
      end;
    end;
  end;
  Result := storage;
end;