c# - 通用约束排除

Question

抱歉问了个愚蠢的问题

是否有可能以可以导出给定 T 的方式对泛型实现约束来自除某些 A、B、C 之外的任何引用类型(其中 A、B、C 是引用类型)。(即)

Where T : class except A,B,C

Answer 1

没有。但是您可以在运行时检查这些类:

public class Foo<T>
{
    static Foo()
    {
        // one of the following depending on what you're trying to do
        if (typeof(A).IsAssignableFrom(typeof(T)))
        {
            throw new NotSupportedException(string.Format(
                "Generic type Foo<T> cannot be instantiated with {0} because it derives from or implements {1}.",
                typeof(T),
                typeof(A)
                ));
        }

        if (typeof(T) == typeof(A))
        {
            throw new NotSupportedException(string.Format(
                "Generic type Foo<T> cannot be instantiated with type {0}.",
                typeof(A)
                ));
        }
    }
}