相关疑难解决方法(0)

为什么这是编译时错误？

public TCastTo CastMe<TSource, TCastTo>(TSource i)
{
     return (TCastTo)i;
}

错误:

annot将类型'TSource'转换为'TCastTo'

为什么这是一个运行时错误？

public TCastTo CastMe<TSource, TCastTo>(TSource i)
{
     return (TCastTo)(object)i;
}

int a = 4;
long b = CastMe<int, long>(a); // InvalidCastException

// this contrived example works
int aa = 4;
int bb = CastMe<int, int>(aa);

// this also works, the problem is limited to value types
string s = "foo";
object o = CastMe<string, object>(s);

我搜索了SO和互联网以获得答案,并找到了类似的通用相关铸造问题的许多解释,但我找不到任何关于这个特殊的简单案例.

是否有某种方法可以将未知数字转换成双倍？例如

    public static double Foo(object obj)
    {
        if (!obj.GetType().IsValueType)
            throw new ArgumentException("Argument should be a number", "obj");
        return (double) obj;
    }

    private static void Main(string[] args)
    {
        double dbl = 10;
        decimal dec = 10;
        int i = 10;
        short s = 10;
        Foo(dbl);
        Foo(dec);
        Foo(i);
        Foo(s);
    }

但是当尝试将unbox打包为不正确的类型时,此代码会抛出异常.