我怎样才能有条件输出参数

Question

The method DoSomething() does Create an Instance of MyClass but not everyone wants to know the MyClass-Object sometimes it also fits if you simply know if the action was successful.

This doesn't compile

public bool DoSomething(out Myclass myclass = null)
{
    // Do something
}

A ref or out parameter cannot have a default value

Sure I could simply remove the out-Keyword but then I needed to assign any variable first, which is not my intention.

This could be a workaround, but i want bool to be the return type

public Myclass DoSomething() //returns null if not successful
{
    // Do something
}

Does anyone know a nice Workaround for that?

Answer 1

Just by overloading:

public bool DoSomething()
{
    myClass i;
    return DoSomething(out i);
}

public bool DoSomething(out myClass myclass)
{
    myclass = whatever;
    return true;
}

And then call DoSomething()

Answer 2

You could wrap the parameter in a class.

class Arguments
{
public Argument () { Arg = null; }
public Myclass Arg { get; set; }
}

and then use it like:

Arguments args;
if (DoSomething (args))
{
  // args.Arg is something
}

and define the function like:

bool DoSomething (Arguments args)
{
  bool success = false;
  if (someaction)
  {
    args.Arg = new Myclass;
    success = true;
  }
  return success;
}

Alternative, and this is making me feel a bit dirty, use exceptions:-

Myclass DoSomething ()
{
  if (someactionhasfailed)
  {
    throw new Exception ("Help");
  }
  return new Myclass;
}

Answer 3

If you do not want to overload the method, you can always create a new class like:

public class Response
    {
    public bool Success{get;set;}
    public Myclass MyclassInstance {get;set;}
    }

And the use it as a return parameter of your DoSomething() method with the following signature:

public Response DoSomething() 
{
    // Do something
}