指定接口只能由引用类型C#实现 [英] Specify that an interface can only be implemented by reference types C#
问题描述
如果我使用C#声明一个接口,有什么方法可以显式声明实现该接口的任何类型都是引用类型?
If I declare an interface in C#, is there any way I can explicitly declare that any type implementing that interface is a reference type?
我要这样做的原因是,无论我在哪里使用接口作为类型参数,都不必指定实现类型也必须是引用类型.
The reason I want to do this is so that wherever I use the interface as a type parameter, I don't have to specify that the implementing type also has to be a reference type.
我要完成的示例:
public interface IInterface
{
void A();
int B { get; }
}
public class UsingType<T> where T : IInterface
{
public void DoSomething(T input)
{
SomeClass.AnotherRoutine(input);
}
}
public class SomeClass
{
public static void AnotherRoutine<T>(T input)
where T : class
{
// Do whatever...
}
}
由于 SomeClass.AnotherRoutine()
的参数必须是引用类型,因此我在调用该方法时会遇到编译器错误,建议我强制使用 T
作为引用类型( UsingType
声明中的,其中T:IInterface,类
).我有什么办法可以在接口级别上强制执行此操作?
As the argument to SomeClass.AnotherRoutine()
is required to be a reference type, I will here get a compiler error where I call the method, suggesting that I force T
to be a reference type (where T : IInterface, class
in the declaration of UsingType
). Is there any way I can enforce this already at the interface level?
public interface IInterface : class
(显然)不起作用,但是也许还有另一种方法可以完成同一件事?
doesn't work (obviously) but maybe there's another way to accomplish the same thing?
推荐答案
如果要在接口下传递某些内容,那么即使您有实现该接口的值类型,如果将其强制转换为接口,其行为也会被装箱.引用类型(因为它装在引用类型中).
If you are passing something around under an interface, then even if you have a value type implementing that interface it will become boxed if cast to the interface and behave like a reference type (because it is boxed inside a reference type).
interface IFoo {
int Value { get; set; }
}
struct Foo : IFoo {
public int Value { get; set; }
}
在用作值类型时观察效果:
Observe the effects when used as a value type:
var a = new Foo() { Value = 3 };
var b = a; // copies value
b.Value = 4;
Console.WriteLine( "a has {0}", a.Value ); //output: a has 3
Console.WriteLine( "b has {0}", b.Value ); //output: b has 4
现在看看将其投射到界面时会发生什么:
Now look what happens when you cast it to the interface:
var a = new Foo() { Value = 3 } as IFoo; //boxed
var b = a; // copies reference
b.Value = 4;
Console.WriteLine( "a has {0}", a.Value ); //output: a has 4
Console.WriteLine( "b has {0}", b.Value ); //output: b has 4
因此,结构或类是否实现接口都没有关系.如果将其强制转换为接口,然后在该接口下传递,则它将作为引用类型.
So it doesn't matter whether a struct or class implements the interface. If cast to the interface and then is passed around under the interface, then it will behave as a reference type.
编辑:因此,如果这些是您的要求...
Edit: So if these are your requirements...
对于X合同:
- 如果结构实现/继承了X,则会引发编译错误.
- X可能不是抽象类.
那么,您就被困住了,因为它们彼此矛盾.
Well, you're simply stuck then, because those contradict each other.
- 如果struct实现/继承协定,则获得编译错误的唯一方法是如果它是抽象类.
- 由于不能使用抽象类来使继承选项保持打开状态,因此必须使用接口.
- 强制执行结构无法实现接口的规则的唯一方法是在运行时.
使用约束其中T:类,IFoo
甚至不能一直工作.如果我有此方法(基于上面相同的 Foo
和 IFoo
):
Using the constraint where T: class, IFoo
wouldn't even work all the time. If I had this method (based on the same Foo
and IFoo
above):
static void DoSomething<T>(T foo) where T: class, IFoo {
foo.Value += 1;
Console.WriteLine( "foo has {0}", foo.Value );
}
然后在这种情况下它将引发编译错误:
Then it would throw a compile error under this circumstance:
var a = new Foo(){ Value = 3 };
DoSomething(a);
但是在这种情况下它会很好地工作:
But it would work just fine under this circumstance:
var a = new Foo(){ Value = 3} as IFoo; //boxed
DoSomething(a);
就我而言,请使用 where T:class,IFoo
样式的约束,然后,只要将其装箱就可以实现结构即可.但是,如果通过盒装结构,则取决于EF进行的检查.也许会起作用.
So as far as I'm concerned, use where T: class, IFoo
-style constraint, and then it may not matter if a struct implements the interface as long as it is boxed. Depends on what checking EF does if passed a boxed struct, though. Maybe it will work.
如果它不起作用,至少通用约束会使您分得一杯part,您可以检查 foo.GetType().IsValueType
(请参阅我的 DoSomething 上面的code>方法)并抛出一个
ArgumentException
来处理盒装结构的情况.
If it doesn't work, at least the generic constraint gets you part-way there, and you can check foo.GetType().IsValueType
(referring to my DoSomething
method above) and throw an ArgumentException
to handle the case of boxed structs.
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