CODEWITHSUNDEEP
c++c++11
Shiqing Shen
Shiqing Shen

Reputation: 85

how can I list-initialize my own class?

I want my own class can be list-initialized like vector: 

myClass a = {1, 2, 3};

How can I do that using C++11 capabilities?

Upvotes: 7

Views: 363

Answers (2)

mementum
mementum

Reputation: 3203

An initializer_list can be (like other STL containers) iterated and the size can be queried. This allows you to do as pointed in the other answer by yuyoyuppe to immediately feed it to a vector. But you may have other intents for your initialization and do something like execute an operation directly on the items of the list without copying.

#include <initializer_list>
#include <iostream>
#include <algorithm>

struct S
{
  int thesum;
  int items;
  S(std::initializer_list<int> l) :
    thesum(std::accumulate(l.begin(), l.end(), 0)),
    items(l.size())
  {}
};

int main()
{
    S s = { 1, 2, 3 };
    std::cout << s.items << std::endl;
    std::cout << s.thesum << std::endl;
    return 0;
}

This prints

3
6

See:

Upvotes: 1

yuyoyuppe
yuyoyuppe

Reputation: 1602

C++11 has a notion of initializer lists. To use it, add a constructor which accepts a single argument of type std::initializer_list<T>. Example:

#include <vector>
#include <initializer_list>
#include <iostream>
struct S
{
  std::vector<int> v_;
  S(std::initializer_list<int> l)
    : v_(l)
  {
    std::cout << "constructed with initializer list of length " << l.size();
  }
};

int main()
{
    S s = { 1, 2, 3 };
    return 0;
}

Upvotes: 8

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