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#include <functional>
#include <iostream>
#include <string>
#include <type_traits>
 
template<typename T, typename F=typename std::function<T()>>
class lazy {
//TYPES
    using uninit_t=typename std::aligned_storage<
            sizeof(T), 
            std::alignment_of<T>::value
        >::type;
//MEMBERS
    F f;
    uninit_t value;
    bool cached { false };
public:
    lazy(F f_) : f { f_ }{  }
 
    T& get() {
        if(!cached) { 
            new(&value) T(f());
            cached=true;
        }   
        return reinterpret_cast<T&>(value); 
    }   
    ~lazy() {
        if(cached)
            get().~T();
    }   
};
 
 
std::string make_big_string() {
    std::cerr << "making string\n";
    return "hello, world";
}
 
template<typename F>
lazy<
    typename std::remove_reference<
        typename std::result_of<F()>::type
    >::type,
    F   
> make_lazy(F f) { return { f }; }
 
int main() {
    auto l_str=make_lazy(make_big_string);
 
 
    std::cout << "get2\t" << l_str.get() << '\n';
    std::cout << "get2\t" << l_str.get() << '\n';
}

prog.cpp:9:11: error: expected nested-name-specifier before 'uninit_t'
prog.cpp:9:11: error: using-declaration for non-member at class scope
prog.cpp:9:19: error: expected ';' before '=' token
prog.cpp:9:19: error: expected unqualified-id before '=' token
prog.cpp:15:5: error: 'uninit_t' does not name a type
prog.cpp:16:10: error: function definition does not declare parameters
prog.cpp: In member function 'T& lazy<T, F>::get()':
prog.cpp:21:13: error: 'cached' was not declared in this scope
prog.cpp:22:18: error: 'value' was not declared in this scope
prog.cpp:25:37: error: 'value' was not declared in this scope
prog.cpp: In destructor 'lazy<T, F>::~lazy()':
prog.cpp:28:12: error: 'cached' was not declared in this scope

Standard output is empty