Question

所以我注意到这段代码有效：

class Program
{
    public static void Main()
    {
        Int32[ ]numbers = {1,2,3,4,5};

        using (var enumerator = Data().GetEnumerator())
        {

        }
    }

    public static IEnumerable<String> Data()
    {
        yield return "Something";
    }
}

特别是，我对using阻止感到好奇，因为：

Int32[] numbers = { 1, 2, 3, 4, 5, 6 };

using (var enumerator = numbers.GetEnumerator())
{

}

因编译错误而失败。显然，yield return返回的类是IDisposable，而常规数组枚举器则不是。所以现在我很好奇：yield return到底创造了什么？

Answer 1

IEnumerator<T>实现了IDisposable，您可以在对象浏览器或MSDN中看到。

非通用IEnumerator没有。

基础Array类实现IEnumerable但不实现IEnumerable<T>。（因为Array不是通用的）
具体数组类型确实实现了IEnumerable<T>，但它们明确地实现了GetEnumerator()（我不确定为什么）。
因此，任何数组类型上的GetEnumerator()可见都会返回IEnumerator。

通用IEnumerable<T>实现返回System.SZArrayHelper.SZGenericArrayEnumerator<T>。

此类的源代码（在Array.cs中）具有以下注释，部分解释了这一点（请记住，对通用数组的所有支持都可以追溯到IEnumerable<T>不反对的时间）

//--------------------------------------------------------------------------------------- 
// ! READ THIS BEFORE YOU WORK ON THIS CLASS. 
//
// The methods on this class must be written VERY carefully to avoid introducing security holes. 
// That's because they are invoked with special "this"! The "this" object
// for all of these methods are not SZArrayHelper objects. Rather, they are of type U[]
// where U[] is castable to T[]. No actual SZArrayHelper object is ever instantiated. Thus, you will
// see a lot of expressions that cast "this" "T[]". 
//
// This class is needed to allow an SZ array of type T[] to expose IList<T>, 
// IList<T.BaseType>, etc., etc. all the way up to IList<Object>. When the following call is 
// made:
// 
//   ((IList<T>) (new U[n])).SomeIListMethod()
//
// the interface stub dispatcher treats this as a special case, loads up SZArrayHelper,
// finds the corresponding generic method (matched simply by method name), instantiates 
// it for type <T> and executes it.
// 
// The "T" will reflect the interface used to invoke the method. The actual runtime "this" will be 
// array that is castable to "T[]" (i.e. for primitivs and valuetypes, it will be exactly
// "T[]" - for orefs, it may be a "U[]" where U derives from T.) 
//---------------------------------------------------------------------------------------

什么样的课程会产生回报

1 个答案: