introduce-parameter-object.md

Introduce Parameter Object

This refactoring changes the interface of a method.

It applies when the method has a large number of parameters that form one or more logical groupings.

It would be better to pass fewer objects that group the data together. This would allow people reading the code to more easily verify that the arguments are passed correctly.

Example

Before

def distance(x1, y1, x2, y2)
  # ...
end

distance(-1, 2, 3, 5)

After

def distance(a, b)
  # ...
end

distance(Point.new(-1, 2), Point.new(3, 5))

Next Steps

Often, this refactoring reveals Feature Envy. If the method deals primarily with data from its parameter object, maybe it should live on that object.