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How many parameters are too many?

Asked 2008-10-06T16:14:48.670
228

Routines can have parameters, that's no news. You can define as many parameters as you may need, but too many of them will make your routine difficult to understand and maintain.

Of course, you could use a structured variable as a workaround: putting all those variables in a single struct and passing it to the routine. In fact, using structures to simplify parameter lists is one of the techniques described by Steve McConnell in Code Complete. But as he says:

Careful programmers avoid bundling data any more than is logically necessary.

So if your routine has too many parameters or you use a struct to disguise a big parameter list, you're probably doing something wrong. That is, you're not keeping coupling loose.

My question is, when can I consider a parameter list too big? I think that more than 5 parameters, are too many. What do you think?

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2 Answers

7

In Worst 5 Code Snippets, check the second one, "Is this a constructor". It has like over 37 ⋅ 4 ≈ 150 parameters:

Here a programmer wrote this constructor [... S]ome of you may think yes its a big constructor but he used eclipse automatic code generation tools[.] NOO, in this constructor there was a tiny bug that I discovered, which made me conclude that this constructor was written by hand. (by the way this is only the top part of the constructor, its not complete).

constructor with over 150 parameters

answered 2010-03-02T08:07:55.030
5

I'd draw the limit for public functions at 5 parameters myself.

IMHO, long parameter lists are only acceptable in private/local helper functions that are only meant to be called from a few specific places in the code. In those cases, you may need to pass a lot of state information along, but readability isn't as big of a concern since only you (or someone who will maintain your code and should understand the fundamentals of your module) have to care about calling that function.

answered 2008-10-06T16:24:29.027

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