Question

With simple values, there is no problem: we simply set them in the .cpp file.

But consider the following example, that require some init/cleanup code:

// .h
class MyClass {
...
private:
    static unsigned First1000Primes[1000];
} ;

In the .cpp file, we want to initialize the array, and need some code for that.

We can define a class Initializer in the .cpp file, with a ctor that fills the values, and declare a static Initializer InitAndCleanup in the same file, so the code will run once at startup (and similarly run dtor/cleanup code if needed).

The problem with this solution is its ‘messiness’, as the initializer has to be a friend of MyClass to access its private parts.

So my question is: is there a cleaner way?

Answer 1

I would say that like everything else, it’s just a matter of encapsulation and packaging.

struct PrimeArray {
    PrimeArray();   // init here
    PrimeArray(PrimeArray const&) = delete;
    PrimeArray& operator=(PrimeArray const&) = delete;
    ~PrimeArray();  // cleanup here

    unsigned data[1000];
};

And then use that:

class MyClass {
public:
    // ...
private:
    static PrimeArray const primes;
};

And initialize in the cpp as usual:

PrimeArray const MyClass::primes{};