kzrdude is referring to the allocation of the Array struct on the heap. It should be something like this instead:

    Array array_create(size_t size, size_t sizeof_data) {
        Array result;
        result.size = size;
        result.capacity = size;
        if(size) {
            result.data = malloc(size * sizeof_data);
        } else {
            result.data = NULL;
        }
        return result;
    }

I think kzrdude is actually referring to the void* pointers that the individual elements of the array live behind. Each of those requires an allocation to insert them, and an extra pointer traversal to read them. In C++ they would live side by side instead, as in regular C arrays. In C you'd need the struct to be redefined for each element type (maybe with another macro) if you wanted the same efficiency.

I'm not seeing that?

In ARRAY_PUSH_BACK, it just inserts the element directly into the buffer, provided there is enough capacity. There is no separate allocation for an element.

You don't need to redefine the struct for each element type, since the macro casts 'data' (type void *) to whatever the array's type is.

You're totally right, I don't know what I was reading >.<

Yes exactly.

This C code is more like `std::unique_ptr<std::vector<T>>`, so now you might see where the extra indirection is located.