C++ /= block

cpp_closure.cpp

#include <functional>
#include <vector>
#include <iostream>

template <typename T>
class Array {
public:
  Array(const std::initializer_list<T> &data)
    : each(*this), keep_if(*this), data(data)
  {}

  struct each_t {
    each_t(Array<T> &parent) : parent(parent) {}
    void operator /= (std::function<void(T)> f) {
      for (auto x : parent.data) { f(x); }
    }
    void operator /= (std::function<void(T, int)> f) {
      for (auto it = parent.data.begin(); it != parent.data.end(); ++it) {
        f(*it, it - parent.data.begin());
      }
    }
    Array<T> &parent;
  } each;

  struct keep_if_t {
    keep_if_t(Array<T> &parent) : parent(parent) {}
    void operator /= (std::function<bool(T)> f) {
      for (auto it = parent.data.begin(); it != parent.data.end(); ++it) {
        if (!f(*it)) {
          it = parent.data.erase(it) - 1;
        }
      }
    }
    Array<T> &parent;
  } keep_if;

private:
  std::vector<T> data;
};

int main() {
  Array<char> array {'a', 'b', 'c', 'd', 'e'};
  array.each /= [](char x){ 
    std::cout << x << std::endl;
  };  
  array.keep_if /= [](char x) {
    return x <= 'c';
  };  
  array.each /= [](char x, int i){ 
    std::cout << i << ":" << x << std::endl;
  };  
}