Method Object Example

Should this just link to FunctorObjectExample? Or is a MethodObject that much different? I'm trying to write one, not sure what the "receiver" might be. Nor do I think I know the best way to return two or more variables. --TerryLorber

This is what I did:

 class MethodObjectExample {
  public:
   MethodObjectExample(int size);
   void compute(std::vector<int>& values, int& response);
  protected:
  private:
   int _size;
 };

 MethodObjectExample::MethodObjectExample(int size) :
   _size(size)
 {
 }// MethodObjectExample

 void
 MethodObjectExample::compute(std::vector<int>& values, int& response)
 {
   // does something that changes values and response based on _size.
   // ... 90 lines of code removed ...
   // done.
 }// compute

---

MethodObject is not a pattern, it is a target of RefactoringImprovingTheDesignOfExistingCode. Start with cruft, such as a very long 90-line method. Write a class called Cruft, and copy all the cruft inside it. Move all the local variables into member variables. Refactor the snot out of the remaining code. Voila: no more cruft.

If you don't start with cruft - if you Refactored early and often, with a very low disgust threshold, you don't get the cruft and don't need MethodObject. After you have MethodObject you are liberated to further split the object into healthier situations. --PhlIp

---

OK, I can see how it's not a pattern, instead a technique used in refactoring. Maybe my question is more of a style thing, What's the best way to return two or more variables from a method? --TerryLorber

Quite possibly this will need to be moved to a different page, but: A standard OO response might be that a method should never return more than one value, because a method should never do more than one thing. If you want to have a method return more than one value, there are a few things you can try:

• Maybe the multiple values can be encapsulated in a single instance. For example, if you want to return an array of [x, y] maybe you really should return an instance of Point.
• Maybe the parts of the algorithm that return the different values can be separated into two different methods and called one after the other. Sometimes this easy; sometimes it's difficult.
• Maybe you should extract part of your code into its own MethodObject. That way you won't need to return values; you can probably just set instance variables and use them.
• Pass in arguments by reference so they can be set in the method rather than use a return value.

When I first started working with OO code I found this rule sort of dogmatic, but these days it's second nature and I almost never run into an instance where it's impractical. (As with many other OO principles, your ability to follow it is directly related to how well your chosen language matches your programming style.) --francis

To elaborate on Francis's first point, this is often a sign that you should create a new class. For example, I often have methods that are responsible for validating some other object according to a set of business rules. Usually, I want two things back from these kinds of methods, a boolean noting whether the item is valid or not, and a list of errors explaining why it is or is not valid. Usually I wrap these up in a simple class called ValidationResult?, which consists of a bool and a collection of strings.

One way to do the transfer in CeePlusPlus is to use a tuple, see for example BoostTupleLibrary. This allows an object which can contain a collection of items of different types e.g. a bool and a string. -- JohnFletcher

Contrast: GodClass

---

CategoryRefactoring