奇数方法行为 - 函数的ToString

Question

Consider this code snippet:

class Program {
  static void Main(string[] args) {
   Console.WriteLine(Test().ToString());
  }

  static IEnumerable<char> Test() {
   foreach (var ch in "test")
    yield return ch;
  }
  static IEnumerable<char> TestOk() {
   return "test";
  }
 }

Test().ToString() returns "ConsoleApplication1.Program+d__0" instead of expected "test".

Test() method isn't even executed - just returns its name! The second method TestOk() works just fine.

What is going on?

Answer 1

它在编译器生成的IEnumerable实现上打印ToString方法 - 迭代器只是语法糖 - 生成IEnumerable的实际实现。

Answer 2

The Test() method returns an IEnumerable(char) which in this case is a compiler generated object. It's ToString() method is the default for an object and returns the type name, also compiler generated.

Answer 3

The yeild return method is treated differently be the compiler - if you check the compiled assembly using reflector whats going on here becomes a little clearer:

private static IEnumerable<char> Test()
{
    return new <Test>d__0(-2);
}

Wheras TestOk returns a string, Test instead returns a class that the compiler generates for you. What you are seeing is the default string representation of that class.

Answer 4

其他答案已经解释了当前的行为，但是如果你想获得预期的行为，那么你可以将IEnumerable<char>转换为数组并使用带有char[]的String构造函数，而不是使用ToString（）：

Console.WriteLine(new string(Test().ToArray()));