How do you return two values from a single method?

Question

When your in a situation where you need to return two things in a single method, what is the best approach?

I understand the philosophy that a method should do one t

Answer 1

If I was returning two of the exact same thing, a collection might be appropriate, but in general I would usually build a specialized class to hold exactly what I needed.

And if if you are returning two things today from those two columns, tomorrow you might want a third. Maintaining a custom object is going to be a lot easier than any of the other options.

Answer 2

If your function has return value(s), it's presumably returning it/them for assignment to either a variable or an implied variable (to perform operations on, for instance.) Anything you can usefully express as a variable (or a testable value) should be fair game, and should dictate what you return.

Your example mentions a row or a set of rows from a SQL query. Then you reasonably should be ready to deal with those as objects or arrays, which suggests an appropriate answer to your question.

Answer 3

Use std::vector, QList, or some managed library container to hold however many X you want to return:

QList<X> getMultipleItems()
{
  QList<X> returnValue;
  for (int i = 0; i < countOfItems; ++i)
  {
    returnValue.push_back(<your data here>);
  }
  return returnValue;
}

Answer 4

For the situation you described, pulling two fields from a single table, the appropriate answer is #4 given that two properties (fields) of the same entity (table) will exhibit strong cohesion.

Your concern that "it might be confusing to create a class just for the purpose of a return" is probably not that realistic. If your application is non-trivial you are likely going to need to re-use that class/object elsewhere anyway.

Answer 5

I have sometimes used continuation-passing style to work around this, passing a function value as an argument, and returning that function call passing the multiple values.

Objects in place of function values in languages without first-class functions.

Answer 6

My choice is #4. Define a reference parameter in your function. That pointer references to a Value Object.

In PHP:

class TwoValuesVO {
  public $expectedOne;
  public $expectedTwo;
}

/* parameter $_vo references to a TwoValuesVO instance */
function twoValues( & $_vo ) {
  $vo->expectedOne = 1;
  $vo->expectedTwo = 2;
}

In Java:

class TwoValuesVO {
  public int expectedOne;
  public int expectedTwo;
}

class TwoValuesTest {
  void twoValues( TwoValuesVO vo ) {
    vo.expectedOne = 1;
    vo.expectedTwo = 2;
  }
}