Question

class GenericWrapper<T>
{   
}

class WrapperInstance : GenericWrapper<string>
{   
}

class Usage
{
    public static Usage Create<T1, T2> (T2 t2) where T1 : GenericWrapper<T2>
    {
        return null;
    }
}

...

// works
Usage.Create<WrapperInstance, string>("bar");

// doesnt work
Usage.Create<WrapperInstance>("bar");

我怀疑答案是没有的,但我是否能够把最后一行汇编起来?

我希望汇编者迫使我提出直截了当的论点,而不必知道或首先去审查<条码>《WrapperInstance,看<条码>>>。

我知道,我可以通过使用第一种方法或以<条码>object作为论据和进行操作时间检查来汇编,但这不是问题;] 我基本上怀疑这些是我唯一的两个选择。

增编

Answer 1

我怀疑答案是没有的,但我是否能够把最后一行汇编起来?

<代码>Create有两个通用参数。你们要么没有具体说明,要么就明确了。如果没有,编辑将试图从援引理由中推断出这些类型。然而,在这种情况下,它不能因为<代码>T1从来不出现在论点清单中。因此,你必须明确这两点。

Answer 2

There are two problems here:

You want to infer just one type argument, and specify the other. You can t do that with normal type inference. However, you could make Usage generic, thus specifying one type argument there, and letting the other be inferred using the generic method:
```
Usage<WrapperInstance>.Create("foo");
```
这是我以前经常做的事,但这只是导致第二个问题......
The type parameter you want to specify (T1) is constrained by the one you want to infer (T2). The above example can t do that, as Usage<WrapperInstance> doesn t "have" a T2 to validate... and you can t constrain an existing type parameter on a generic method - only ones which are introduced in the method.

我认为,我们有一种方式: 为此:

public class Usage
{
    public static Usage<T2> For<T2>(T2 t2)
    {
        return new Usage<T2>(t2);
    }
}

public class Usage<T2>
{
    private readonly T2 t2; // Assuming we need it

    public Usage(T2 t2)
    {
        this.t2 = t2;
    }

    // I don t know what return type you really want here
    public static Foo Create<T1>() where T1 : GenericWrapper<T2>
    {
        // Whatever
    }
}

你们也这样做:

Usage.Foo("bar").Create<WrapperInstance>();

在不了解你试图做些什么的情况下,我不知道这是否有用——但does <>/em>设法完成你在以下各方面的工作:

Validating the WrapperInstance type argument

Inferring the string type argument

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