oop - Reducing the number of arguments to a constructor

Question

I am reading "Clean Code" and having trouble figuring out how to keep some of my functions (usually constructors) to their MAXIMUM of 3 parameters.

Often my objects need an awful lot of information to work - am I supposed to make a small constructor and then use mutator functions to give them all of the information? This doesn't seem any better than just using a big constructor.

As an example, I have a "MovablePatch" class. It lets the user drag a square around in a window. It needs a several parameters, including Radius, Color, Renderer, InitialPosition, and Visibility. Currently I collect all of these from my GUI and then call:

MovablePatch(int radius, Renderer* renderer, Color color,  Position initial, bool visibility)

These are only some of the things that I need in this class. Can anyone suggest how else I might package this information to pass to the constructor? I don't see any obvious "break it into smaller classes" appearing here.

question from:https://stackoverflow.com/questions/8672164/reducing-the-number-of-arguments-to-a-constructor

Answer 1

Do not take maxims like "thou shalt not have more than 3 parameters in thy constructors" at face value. If you have the slightest chance of making an object immutable, make it; and if it being immutable means that it is going to have a constructor with 50 parameters, so be it; go for it; don't even think about it twice.

Even if the object is going to be mutable, still, you should pass its constructor as many parameters as necessary so that immediately upon construction it will be in a valid and meaningful state. In my book, it is absolutely impermissible to have to know which are the magic mutator methods that have to be called (sometimes even in the right order) before any other methods can be invoked, under penalty of segfault.

That having been said, if you would really like to reduce the number of parameters to a constructor, or to any function, simply pass this method an interface that it can invoke to get from it the stuff it needs in order to work.