Passing single object vs. passing multiple parameters

Question

Suppose I have the following

Class A {
    Foo getFoo();
    Bar getBar();
    Baz getBaz();
}

And I need to define a function doStuff that uses Foo, Bar, Baz of one object and does some stuff

I'm struggling between which method of implementing doStuff is better (suppose it would be undesirable to place doStuff inside class A)

Method A

void doStuff(Foo foo, Bar bar, Baz baz)
{ 
    //some operation
}

or

Method B

void doStuff(A a)
{
    Foo foo = a.getFoo();
    Bar bar = a.getBar();
    Baz baz = a.getBaz();
    //some operation
}

To my limited knowledge, (+ pros, - cons)

Method A

+It is clear exactly what parameters doStuff() operates on

-Susceptible to long parameter lists and more susceptible to user mistakes

Method B

+Simple, easy to use method

+Seems more extensible (?)

-Creates unnecessary dependency towards class A

---

Can anyone share additional insight towards the pros and cons of these two methods?

Answer 1

Method A (naked parameters) always has the advantages that

• it requires the method author to type less, since they don't have to implement a Parameter Object,
• it requires the method caller to type less, since they don't have to instantiate a Parameter Object
• it performs better, since no Parameter Object has to be constructed and garbage collected
• the reader can see what the individual parameters are from the method signature alone (but this is a double-edged sword; see below)

Method B (Parameter Object) has advantages when

• the parameters have domain meaning as a group, so the Parameter Object can be given a name that explains that meaning, saving the reader from having to read and understand each member of the group and how they relate
• the parameter list is used in more than one method, so using the Parameter Object in each reduces duplication
• the values in the parameter list are passed around among multiple methods as a group, which is easier when they can be passed as a single Parameter Object
• some combinations of values are invalid; the Parameter Object can prevent those combinations
• some values are optional, which can be provided by the Parameter Object instead of (depending on your language) default parameter values or overloaded methods
• there is more than one parameter of the same type, making value-swapping errors more likely (although a Parameter Object is not better in this case if it has a constructor with the same parameter list as the method)

That the Parameter Object introduces a new dependency on which caller and callee depend is not much of a disadvantage, since it is a simple class with no dependencies of its own.

So, Parameter Object is

• almost never worthwhile for a single parameter, sometimes worthwhile for a two-parameter method (e.g. Point is usually better than x, y) and sometimes not, and increasingly helpful with three and more parameters
• increasingly helpful when more methods use the same parameter list