使用Cast将int[]转换为double[] ?(复制)

Possible Duplicate:
IEnumerable.Cast<>

可能的重复:IEnumerable.Cast < >

One can implicitly convert from int to double. Why does "Specified cast is not valid." exception is raised here?

可以隐式地将int转换为double。为什么“指定的强制类型转换无效”在这里引发异常?

 double[] a = Enumerable.Range(0, 7).Cast<double>().ToArray();

I have tried several "versions" of it.

我试过几个“版本”。

P.S. I know possible solutions like:

附注:我知道可能的解决办法，比如:

 double[] a = Enumerable.Range(0, 7).Select(x => (double)x).ToArray();

But I'm curious how Cast works => why it doesn't work in this example which looks so obvious.

但是我很好奇Cast是如何工作的=>为什么在这个看起来很明显的例子中它不工作。

2 个解决方案

#1

Cast is made to turn an IEnumerable (untyped) to an IEnumerable<T> (generically typed). It won't actually differently-cast any of the members.

Cast被用来将IEnumerable(非类型化)转换为IEnumerable (T>)(泛型)。它不会有任何不同的成员。

Per this answer:

每一个答案:

Well, you have incorrect expectations of Cast, that's all - it's meant to deal with boxing/unboxing, reference and identity conversions, and that's all. It's unfortunate that the documentation isn't as clear as it might be

你对角色的期望是错误的，仅此而已——它是用来处理装箱/拆箱、引用和身份转换的，仅此而已。不幸的是，文档并不像它可能的那样清晰

So, you're stuck with .Select().

因此，您被困在了。select()中。

#2

The reason this fails is because essentially you're doing this:

失败的原因是因为你在做这个:

        int x = 10;
        object f = x;
        double d = (double) f;

The int is getting boxed into the object, and when you go to unbox it, you're trying to unbox it to a double.

int被装入对象中，当你打开它时，你试图将它打开到double。

More specifically, here's the implementation of Cast:

更具体地说，这是Cast的实现:

public static IEnumerable<TResult> Cast<TResult>(this IEnumerable source)
{
    IEnumerable<TResult> enumerable = source as IEnumerable<TResult>;
    if (enumerable != null)
    {
        return enumerable;
    }
    if (source == null)
    {
        throw Error.ArgumentNull("source");
    }
    return Enumerable.CastIterator<TResult>(source);
}

private static IEnumerable<TResult> CastIterator<TResult>(IEnumerable source)
{
    foreach (object current in source)
    {
        yield return (TResult)current;
    }
    yield break;
}

As you can see, it's looping through the IEnumerable and boxing each element in the source. It then tries to unbox at which point you blow up.

如您所见，它通过IEnumerable接口进行循环，并对源代码中的每个元素进行装箱。然后它试着打开你爆炸的地方。

#1