Do you consider multiple initialization steps "poor form"?

Question

I'm writing a physics simulation (Ising model) in C++ that operates on square lattices. The heart of my program is my Ising class with a constructor that calls for the row and column dimensions of the lattice. I have two other methods to set other parameters of the system (temperature & initial state) that must get called before evolving the system! So, for instance, a sample program might look like this

int main() {
    Ising system(30, 30);
    system.set_state(up);
    system.set_temperature(2);

    for(int t = 0; t < 1000; t++) {
        system.step();
    }

    return 0;
}

If the system.set_*() methods aren't called prior to system.step(), system.step() throws an exception alerting the user to the problem. I implemented it this way to simplify my constructor; is this bad practice?

Answer 1

It is recommended to put all mandatory parameters in the constructor whenever possible (there are exceptions of course, but these should be rare - I have seen one real-world example so far). This way you make your class both easier and safer to use.

Note also that by simplifying your constructor you make the client code more complicated instead, which IMO is a bad tradeoff. The constructor is written only once, but caller code may potentially need to be written many times more (increasing both the sheer amount of code to be written and the chance of errors).

Answer 2

Not at all, IMO. I face the same thing when loading data from external files. When the objects are created (ie, their respective ctors are called), the data is still unavailable and can only be retrieved at a later stage. So I split the initialisation in different stages:

1. constructor
2. initialisation (called by the framework engine when an object is activated for the first time)
3. activation (called each time an object is activated).

This is very specific to the framework I'm developing, but there is no way to deal with everything using just the constructor.

However, if you know the variables at the moment the ctor is called, it's better not to complicate the code. It's a possible source of headaches for anyone using your code.

Answer 3

IMO this is poor form if all of these initialization steps must be invoked every time. One of the goals of well-designed software is to minimize the opportunities to screw up, and having multiple methods which must be invoked before an object is "usable" simply makes it harder to get right. If these calls were optional then having them as separate methods would be fine.

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