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Custom emplace

对于custom container，如何实现emplace呢？在前面的章节中，我们已经知道emplace的实现所依赖于语言特性。

下面分别对我们custom container的两种方式中，如何custom emplace来进行说明。

Wrapper of STL container

对于基于STL container 进行封装实现的custom container，由于STL container 一般都实现了emplace，因此，programmer可以直接进行调用，下面是一些例子。

stackoverflow Custom Container emplace with variadic templates

A

In case anyone stumbles upon the same issue, this is how I achieved this:

void emplace(Args&&... args) {
    ++Count;
    ++_indexWrite;
    if (_indexWrite > _size - 1) _indexWrite = 0;
    _v.emplace(_v.begin() + _indexWrite, std::forward<Args>(args)...);
}

Although what I really wanted was to construct an element using the reserved memory in that index, and not inserting a new element at that specific position.

stackexchange Perfect-forwarding while implementing emplace

#include <set>
using namespace std;

template<typename T>
class myset {
  std::set<T> m_s;
  typedef typename std::set<T>::iterator iterator;
  int cnt;
public:
  template <class... Args>
  pair <iterator,bool> emplace ( Args&&... args ) {
    pair<iterator,bool> p = m_s.emplace(std::forward<Args>(args)...);
    if (p.second) //true if a new element was inserted
      cnt ++; //house keeping
    return p;
  }
};

int main() {myset<int> s;}