CODEWITHSUNDEEP
c#c#-4.0
ddt
ddt

Reputation: 43

Odd method behavior - ToString of a function

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?

Upvotes: 4

Views: 155

Answers (4)

Quartermeister
Quartermeister

Reputation: 59149

The other answers have explained the current behavior, but if you want to get your expected behavior then instead of using ToString() you can convert the IEnumerable<char> to an array and use the String constructor that takes a char[]: 

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

Upvotes: 0

Justin
Justin

Reputation: 86779

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.

Upvotes: 2

bbudge
bbudge

Reputation: 1137

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.

Upvotes: 2

On Freund
On Freund

Reputation: 4436

It's printing the ToString method on the IEnumerable implementation generated by the compiler - Iterators are just syntactic sugar - a real implementation of IEnumerable is generated.

Upvotes: 7

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