Implementing Array Initializer

Question

You can declare and initialize regular arrays on the same line, like so:

int PowersOfTwo[] = {1, 2, 4, 8, 16, 32, 64, 128};

Is there a way to replicate this behavior in custom classes? So, for example:

MyClass<int> PowersOfTwo = {1, 2, 4, 8, 16, 32, 64, 128};

You can have a copy constructor take an array as its parameter, but you still have to declare the array on the previous line.

int InitializationArray[] = {1, 2, 4, 8, 16, 32, 64, 128};
MyClass<int> PowersOfTwo = InitializationArray; 

Answer 1

You can implement your class in such a way that you can write this:

MyClass<int> array;
array = 1,2,3,4,5,6,7,8,9,10;//dont worry - all ints goes to the array!!!

Here is my implementation:

template <class T>
class MyClass
{
   std::vector<T> items;
public:

    MyClass & operator=(const T &item)
    {
       items.clear();
       items.push_back(item);
       return *this;
    }
    MyClass & operator,(const T &item)
    {
       items.push_back(item);
       return *this;
    }
    size_t Size() const { return items.size(); }
    T & operator[](size_t i) { return items[i]; }
    const T & operator[](size_t i) const { return items[i]; }

};

int main() {

        MyClass<int> array;
        array = 1,2,3,4,5,6,7,8,9,10;
        for (size_t i = 0 ; i < array.Size() ; i++ )
           std::cout << array[i] << std::endl;
        return 0;
}

Output:

1
2
3
4
5
6
7
8
9
10

See online demo : http://www.ideone.com/CBPmj

Two similar solutions you can see here which I posted yesterday :

Template array initialization with a list of values

---

EDIT:

Similar tricks you can do to populate existing STL containers. For example, you can write this:

std::vector<int> v;
v+=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15; //push_back is called for each int!

All you need to overload () and , operator as:

template<typename T>
std::vector<T>& operator+=(std::vector<T> & v, const T & item)
{
    v.push_back(item); return v;
}
template<typename T>
std::vector<T>& operator,(std::vector<T> & v, const T & item) 
{
    v.push_back(item); return v;
}

Working demo : http://ideone.com/0cIUD

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AGAIN EDIT:

I'm having fun with C++ operator. Now this:

std::vector<int> v;
v << 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15; //inserts all to the vector!

I think this looks better!