类型X的参数必须支持接口Y. [英] Parameter of type X must support interface Y

问题描述

  IBuilder = interface（IInvokable）
 end; 
 
 IBuilder< T：IBuilder; TOut：TWinControl> = interface（IInvokable）
 end; 
 
 TBuilder< T：IBuilder; TOut：TWinControl> = class（TInterfacedObject，IBuilder，IBuilder< T，TOut>）
 end; 
 
 TBuilder = class（TBuilder< TBuilder，TWinControl>）
 end; 
  

这种结构允许我创建一个糖语法，如下所示：

  TBuilder< T：IBuilder; TOut：TWinControl> = class（TInterfacedObject，IBuilder，IBuilder< T，TOut>）
 
函数输出：TOut; 
函数名称（aName：string）：T; 
函数Left（aLeft：Integer）：T; 
函数Top（aTop：Integer）：T; 
 
 end; 
 $ b $ // ...稍后
 
 TBuilder.Create（）。Left（10）.Top（5）.Name（'ABC'）; //很好的一行
  

问题是我收到一个编译错误，说

  E2514类型参数TBuilder必须支持'IBuilder'接口。 
  

这可能是由于类型化约束 T：IBuilder 出现在界面上，即使TBuilder支持IBuilder（通过它的祖先）。

任何人都可以请我指导如何解决这个问题吗？

虽然我不能使用 TBuilder = class（TBuilder< IBuilder，TObject>）

解决方案

这是无法完成的。你基本上是这样做的：

  IBar = interface（IInterface）end; 
 
 TFoo< T：IBar> = class（TObject，IBar）end; 
 
 TBar = TFoo< TBar>; 
  

其中产生错误

E2086类型'TBar'尚未完全定义

如果没有接口依赖性，您可以将其写为

  TBar = class（TFoo< TBar>）end; 
  

使其成为真正的后代，而不仅仅是一个别名。这通常可以解决该类型，但接口依赖性迫使编译器提出以下问题： TBar 支持 IBar


如果你仔细想想，可以这样解释：

  TBar = TFoo< TBar> {TBar支持IBar？} 
 | 
 TBar = TFoo< TBar> ... {ok，TBar支持IBar？} 
 | 
 TBar = TFoo< TBar> {ok，TBar支持IBar？} 
 | 
 {... turtles一路下来} 
  

您要求编译器解决无限递归问题。它不能做到这一点。

I have a setup like so :

IBuilder = interface(IInvokable)
end;

IBuilder<T: IBuilder; TOut : TWinControl> = interface(IInvokable)
end;

TBuilder<T: IBuilder; TOut : TWinControl> = class(TInterfacedObject, IBuilder, IBuilder<T, TOut>)
end;

TBuilder = class(TBuilder<TBuilder, TWinControl>)
end;

This kind of structure allows me to build a sugar syntax like so :

TBuilder<T : IBuilder; TOut : TWinControl> = class(TInterfacedObject, IBuilder, IBuilder<T, TOut>)

  function Output : TOut;
  function Name(aName : string) : T;
  function Left(aLeft : Integer) : T;
  function Top(aTop : Integer) : T;

end;

// ... later

TBuilder.Create().Left(10).Top(5).Name('ABC'); // Nice one liner

The problem is that I get a compilation error, saying that

E2514 The type parameter TBuilder must support interface 'IBuilder'.

This is probably due to the typed constraint T: IBuilder present on the interface, even though TBuilder does support IBuilder (trough it's ancestor).

Can anyone please direct me on how to get around this?

Though, I cannot use TBuilder = class(TBuilder<IBuilder, TObject>)

解决方案

This can't be done. You're essentially trying to do this :

  IBar = interface(IInterface) end; 

  TFoo<T : IBar> = class(TObject, IBar) end;

  TBar = TFoo<TBar>;

Which generates error

E2086 Type 'TBar' is not yet completely defined

Without the interface dependence you can write this as

 TBar = class(TFoo<TBar>) end;

making it a true descendent and not just an alias. This could normally resolve the type, but the interface dependence is forcing the compiler to ask the question : Does TBar support IBar?

If you think about it, this works out as :

TBar = TFoo<TBar>   {TBar support IBar?}  
             |
             TBar = TFoo<TBar>... {ok, TBar support IBar?}
                          |
                         TBar = TFoo<TBar> {ok, TBar support IBar?}
                                      |
                                      {...turtles all the way down}

You're asking the compiler to solve an infinite recursion problem. It cannot do this.

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