Generic Casting

问题

I suspect the answer is no, but is it possible to do something like this in C#.NET (v2.0).

class Converter<E>
{
    public E Make(object o)
    {
        return o as E;
    }
}

If not, is it possible to check types like this:

public bool IsType(object o, Type t)
{
    return o is E;
}

I'm not certain about the terminology so it is rather hard to Google for me. But my guess is that these two problems are related. Any ideas?

回答1:

You can cast o to E using the () Operator:

class Converter<E>
{
    public E Make(object o)
    {
        return (E)o;
    }
}

If you use as, o as E requires E to a be a reference type, because if o is not castable to E, the result is (E)null. You can constrain E to reference types by using the class Constraint:

class Converter<E> where E : class
{
    public E Make(object o)
    {
        return o as E;
    }
}

---

public bool IsType(object o, Type t)
{
    return (o != null) ? t.IsAssignableFrom(o.GetType()) : t.IsClass;
}

来源：https://stackoverflow.com/questions/9443951/generic-casting