Question

Let’s say I have a class with an expensive constructor, and let’s say I don’t need to create the constructor because it’s “simple”. Inside the class, I want to put a typedef. All together, it looks like:

class Expensive {
public:
    typedef double data_type;
    data_type data[100000][100000];
};

Now, in my calling code, if I do:

Expensive::data_type singleValue;

is that going to create a temporary instance of Expensive and allocate all that space for the data just to get access to the typedef?

Answer 1

Simply put: No. The operation has no runtime effect whatsoever. Even just declaring a double is not guaranteed to have any effect at runtime as along as you are not using it 😉