how-to initialize 'const std::vector' like a c array

Question

Is there an elegant way to create and initialize a const std::vector like const T a[] = { ... } to a fixed (and small) number of val

Answer 1

Short and dirty way (similar to Boost's list_of())

#include 
#include 
#include 
#include 
using namespace std;

template 
struct vlist_of : public vector {
    vlist_of(const T& t) {
        (*this)(t);
    }
    vlist_of& operator()(const T& t) {
        this->push_back(t);
        return *this;
    }
};

int main() {
    const vector v = vlist_of(1)(2)(3)(4)(5);
    copy(v.begin(), v.end(), ostream_iterator(cout, "\n"));
}

Now, C++11 has initializer lists, so you don't need to do it that way or even use Boost. But, as an example, you can do the above in C++11 more efficiently like this:

    #include 
    #include 
    #include 
    #include 
    using namespace std;

    template 
    struct vlist_of : public vector {
        vlist_of(T&& t) {
            (*this)(move(t));
        }
        vlist_of& operator()(T&& t) {
            this->push_back(move(t));
            return *this;
        }
    };

    int main() {
        const vector v = vlist_of(1)(2)(3)(4)(5);
        for (const auto& i: v) {
            cout << i << endl;
        }
    }

But, it's still not as efficient as using a C++11 initializer list because there's no operator=(vlist_of&&) defined for vector.

tjohns20's way modified like the following might be a better c++11 vlist_of:

#include 
#include 
#include 
using namespace std;

template 
class vlist_of {
    public:
        vlist_of(T&& r) {
            (*this)(move(r));
        }
        vlist_of& operator()(T&& r) {
            v.push_back(move(r));
            return *this;
        }
        vector&& operator()() {
            return move(v);
        }
    private:
        vector v;
    
};

int main() {
    const auto v = vlist_of(1)(2)(3)(4)(5)();
    for (const auto& i : v) {
        cout << i << endl;
    }
    
}