002_grammar_aligned_storage.cpp

#include <iostream>
#include <type_traits>
#include <string>
 
template<class T, std::size_t N>
class static_vector
{
    // properly aligned uninitialized storage for N T's
    typename std::aligned_storage<sizeof(T), alignof(T)>::type data[N];
    std::size_t m_size = 0;
 
public:
    // Create an object in aligned storage
    template<typename ...Args> void emplace_back(Args&&... args) 
    {
        if( m_size >= N ) // possible error handling
            throw std::bad_alloc{};
 
        // construct value in memory of aligned storage
        // using inplace operator new
        new(&data[m_size]) T(std::forward<Args>(args)...);
        ++m_size;
    }
 
    // Access an object in aligned storage
    const T& operator[](std::size_t pos) const 
    {
        // note: needs std::launder as of C++17
        return *reinterpret_cast<const T*>(&data[pos]);
    }
 
    // Delete objects from aligned storage
    ~static_vector() 
    {
        for(std::size_t pos = 0; pos < m_size; ++pos) {
            // note: needs std::launder as of C++17
            reinterpret_cast<T*>(&data[pos])->~T();
        }
    }
};
 
int main()
{
    static_vector<std::string, 10> v1;
    v1.emplace_back(5, '*');
    v1.emplace_back(10, '*');
    std::cout << v1[0] << '\n' << v1[1] << '\n';
}