Delphi - 接口继承与泛型 [英] Delphi - Interface inheritance with generics

问题描述

我目前遇到编译错误，我们公司没有人可以帮助，我很遗憾的是找不到SO或谷歌的正确搜索模式。

作为代码我正在使用2个接口，继承和2类，继承。
以下代码重现错误：

 程序Project22; 
 
 {$ APPTYPE CONSOLE} 
 type 
 IStorageObject = interface（IInterface）
 end; 
 TObjectStorage< T：IStorageObject> = class（TObject）
 end; 
 IKeyStorageObject< TKey> = interface（IStorageObject）
 end; 
 TKeyObjectStorage< TKey，T：IKeyStorageObject< TKey>> = class（TObjectStorage< T>）
 end; 
 TImplementingClass< TKey> = class（TInterfacedObject，IKeyStorageObject< TKey>）
 end; 
 begin 
 TKeyObjectStorage< Integer，TImplementingClass< Integer>> .Create; 
结束。 
  

'TKeyObjectStorage'的编译器错误是：

[DCC错误] Project22.dpr（11）：E2514类型参数'T'必须支持IStorageObject接口

我认为是编译器没有正确地识别Class'TKeyObjectStorage'的参数T。
它应该是正确的，因为想要的类型'IKeyStorageObject'具有父类型IStorageObject。

为什么这不起作用？我究竟做错了什么？这是不可能在德尔福？

解决方案

更新

原来的问题有一个我确定的问题（见下文）。但是，我描述的修复对于XE3和更高版本是很好的，但下面的程序不能在XE2中编译。因此，我得出结论，这是一个XE2泛型编译器错误。

无论如何，以下是 Delphi XE2 的解决方法：

  {$ APPTYPE CONSOLE} 
 type 
 IStorageObject = interface（IInterface）
 end; 
 TObjectStorage< T：IStorageObject> = class（TObject）
 end; 
 IKeyStorageObject< TKey> = interface（IStorageObject）
 end; 
 TKeyObjectStorage< TKey; T：IKeyStorageObject< TKey>，IStorageObject> = class（TObjectStorage< T>）
 end; 
 TImplementingClass< TKey> = class（TInterfacedObject，IStorageObject，IKeyStorageObject< TKey>）
 end; 
 begin 
 TKeyObjectStorage< Integer，TImplementingClass< Integer>> .Create; 
结束。 
  

---

原始答案 / p>

如果您提供了一个展示编译器错误的完整程序，这将会更好。您需要尝试实例化一个对象才能看到该错误。

但是，我想我已经转载了你的问题。所以我相信问题是这个代码：

  TKeyObjectStorage< TKey，T：IKeyStorageObject&TK;>> = ... 
  

将通用约束应用于 TKey 和 T 。现在，显然你只希望约束适用于 T ，所以你需要写：

  TKeyObjectStorage< TKey; T：IKeyStorageObject< TKey>> = ... 
  

这是一个简短的程序，根据 Delphi XE3 ：

  {$ APPTYPE CONSOLE} 
 type 
 IStorageObject = interface（IInterface）
结束
 TObjectStorage< T：IStorageObject> = class（TObject）
 end; 
 IKeyStorageObject< TKey> = interface（IStorageObject）
 end; 
 TKeyObjectStorage< TKey; T：IKeyStorageObject< TKey>> = class（TObjectStorage< T>）
 end; 
 TImplementingClass< TKey> = class（TInterfacedObject，IKeyStorageObject< TKey>）
 end; 
 begin 
 TKeyObjectStorage< Integer，TImplementingClass< Integer>> .Create; 
结束。 
  

这是一个细微差别，将逗号更改为分号。通过重要的标点符号编程从来没有太多的乐趣。那就是说，你熟悉在形式参数列表中的逗号和分号之间的区别，所以它不应该是太多的惊喜，看到这里同样的区别。

文档确实涵盖了这一点：

多个类型参数

指定约束时，可以将多个类型参数分隔
分号，与参数列表声明一样：

 键入
 TFoo< T：ISerializable;五：IComparable> 
  

像参数声明一样，多个类型参数可以通过逗号列表绑定
同样的限制：

 键入
 TFoo< S，U：ISerializable> ... 
  

在上面的例子中， S 和 U 都绑定到 ISerializable
约束。

I am currently stuck with a compiling error, no one in our company can help and I am sadly not finding the correct search patterns for SO or google.

As code I am using 2 Interfaces, inherited and 2 Classes, inherited. The following code reproduces the error:

program Project22;

{$APPTYPE CONSOLE}
type
  IStorageObject = interface(IInterface)
  end;
  TObjectStorage<T: IStorageObject> = class(TObject)
  end;
  IKeyStorageObject<TKey> = interface(IStorageObject)
  end;
  TKeyObjectStorage<TKey, T: IKeyStorageObject<TKey>> = class(TObjectStorage<T>)
  end;
  TImplementingClass<TKey> = class(TInterfacedObject, IKeyStorageObject<TKey>)
  end;
begin
  TKeyObjectStorage<Integer, TImplementingClass<Integer>>.Create;
end.

The compiler error for 'TKeyObjectStorage' is:

[DCC Error] Project22.dpr(11): E2514 Type parameter 'T' must support interface 'IStorageObject'

What I think is, that the compiler is not recognizing that Parameter T of the Class 'TKeyObjectStorage' correctly. It should be correct, since the wanted Type 'IKeyStorageObject' has the parent type IStorageObject.

Why is this not working? What am I doing wrong? Is this not possible in Delphi?

解决方案

Update

The original question had a problem which I identified (see below). However, the fix I describe there is fine for XE3 and later, but that program below does not compile in XE2. Thus I conclude that this is an XE2 generics compiler bug.

Anyway, here's a workaround for Delphi XE2:

{$APPTYPE CONSOLE}
type
  IStorageObject = interface(IInterface)
  end;
  TObjectStorage<T: IStorageObject> = class(TObject)
  end;
  IKeyStorageObject<TKey> = interface(IStorageObject)
  end;
  TKeyObjectStorage<TKey; T: IKeyStorageObject<TKey>, IStorageObject> = class(TObjectStorage<T>)
  end;
  TImplementingClass<TKey> = class(TInterfacedObject, IStorageObject, IKeyStorageObject<TKey>)
  end;
begin
  TKeyObjectStorage<Integer, TImplementingClass<Integer>>.Create;
end.

---

Original answer

It would have been better if you had provided a complete program that exhibited the compiler error. You need to attempt to instantiate an object to see that error.

But, I think I've reproduced your problem. So I believe that the issue is that this code:

TKeyObjectStorage<TKey, T: IKeyStorageObject<TKey>> = ...

applies the generic constraint to both TKey and T. Now, clearly you only want the constraint to apply to T so you'll need to write:

TKeyObjectStorage<TKey; T: IKeyStorageObject<TKey>> = ...

Here's a short program that compiles following the change in Delphi XE3:

{$APPTYPE CONSOLE}
type
  IStorageObject = interface(IInterface)
  end;
  TObjectStorage<T: IStorageObject> = class(TObject)
  end;
  IKeyStorageObject<TKey> = interface(IStorageObject)
  end;
  TKeyObjectStorage<TKey; T: IKeyStorageObject<TKey>> = class(TObjectStorage<T>)
  end;
  TImplementingClass<TKey> = class(TInterfacedObject, IKeyStorageObject<TKey>)
  end;
begin
  TKeyObjectStorage<Integer, TImplementingClass<Integer>>.Create;
end.

This is quite a nuance, the changing of a comma to a semi-colon. Programming by significant punctuation is never much fun. That said, you are familiar with the difference between commas and semi-colons in formal parameter lists and so it should not come as too much of a surprise to see the same distinction drawn here.

The documentation does cover this mind you:

Multiple Type Parameters

When you specify constraints, you separate multiple type parameters by semicolons, as you do with a parameter list declaration:

type
  TFoo<T: ISerializable; V: IComparable>

Like parameter declarations, multiple type parameters can be grouped together in a comma list to bind to the same constraints:

type
  TFoo<S, U: ISerializable> ...

In the example above, S and U are both bound to the ISerializable constraint.

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