Implementing efficient insertion on a custom unordered_map container in C++

I am creating a custom C++ STL Container library and I have a question that concerns efficient insertion both in code size and execution time (avoiding as many copies as possible).

I want to write an insert (same applies for find/erase) function (_insert_unique) that can be called from other insert-like functions and also preserve their semantics.

For example :

    std::pair<iterator, bool> insert(const value_type &val) {
        return _insert_unique(val);
    }

    std::pair<iterator, bool> insert(value_type &&val) {
        return _insert_unique(std::move(val));
    }

    template <class... Args>
    std::pair<iterator, bool> emplace(Args&&... args) {
       return _insert_unique(std::forward<Args>(args)...);
    }

By preserving the semantics I mean that this function should avoid making copies when the parameter is value_type&& or avoid constructing a key in emplace() if the key doesn't already exist in the set (I know that the C++11 emplace() version requires some workaround on this by using "forward_as_tuple" and "piecewise_construct" and that a new function try_emplace() was introduced afterwards for this purpose).

So my question is if I can achieve the functionality I want without writing duplicate code for every insert-like function.