为什么我会收到InvalidCastException的？ [英] Why am I getting InvalidCastException?

问题描述

我在C＃下面的代码片段

I have following code snippet in c#

List<int> list = new List<int>() { 1, 23, 5, 3, 423, 3 };
            var query = list.Cast<double>().Select(d => d);
            try
            {
                foreach (var item in query)
                {
                    Console.WriteLine(item);

                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);

            }

这是编译完美，但是当我执行这个我越来越例外。

It's compile perfectly,but when i am executing this I am getting exception.

推荐答案

由于您是从一个int类型转换翻一番，这不是它的一个类型转换转换，这是从当你施放INT在一般情况下翻番有所不同

Because you're typecasting from an int to double, it's not a conversion it's a type cast and this is somewhat different from when you cast int to double in the general case.

演员LT; T> 扩展方法的用途在IL指令 unbox.any

The Cast<T> extension method uses the IL instruction unbox.any

尽管C＃铸像这样

var x = (double)42;

实际上会导致IL指令

Actually results in the IL instruction

conv.r8 

从根本上拆箱的类型，不同的类型错了，这就是为什么你得到的异常。

Fundamentally unboxing an type as a different type is wrong and that's why you get the exception.

的这个问题有相同的答案，并链接到的博客文章通过埃里克利珀。

This question has the same answer and also links to a blog post by Eric Lippert.

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