Microsoft.CSharp.RuntimeBinder.RuntimeBinderException：'IInterface'不包含'XMethod'的定义

Question

我有以下接口及其继承：

public interface IBase1<T>  where T : struct
{}

public interface IBase2<T>  where T : struct
{
 T XMethod();
}

public interface IBaseInt : IBase1<int>, IBase2<int>
{}

public interface IBaseDecimal : IBase1<decimal>, IBase2<decimal>
{}

public interface IBaseInner<T>
{
void InnerMethod();
}

然后我有一个实现IBaseInt和IBaseInner

的类

public class BaseInt : IBaseInt, IBaseInner<int>
{
// some implementation code here

public int XMethod()
{
// implementation of int Xmethod
}

public void InnerMethod()
{
// implementation of InnerMethod
}
}

其他，实现IBaseDecimal和IBaseInner

public class BaseDecimal : IBaseDecimal, IBaseInner<decimal>
{
    private readonly IBaseInt baseInt; //Injected by ninject
    public BaseDecimal(IBaseInt pBaseInt)
    {
        this.baseInt = pBaseInt;
    }

        public decimal XMethod()
        {
        // implementation of decimal XMethod
        }
        public void InnerMethod()
        {
            baseInt.XMethod(); // throws an exception, because don't recognize this method
        }
    }

但如果我通过明确的演员来电话：

(baseInt as IBase2).XMethod();

不抛出异常。

你能解释一下为什么会这样吗？