singleton.hpp

#include <iostream>
#include <string>
#include <memory>
#include <cassert>

template <class T>
class Singleton 
{
public:
    using Type = typename std::remove_all_extents<T>::type;

    template <typename ...Args>
    Singleton(Args&& ...args)
    {
        struct StaticObjCreator {
            StaticObjCreator(std::unique_ptr<Type>& obj_ptr, Args&& ...arguments) {
                assert(obj_ptr == nullptr);
                obj_ptr.reset(new Type(std::forward<Args>(arguments)...));
            }
        };
        static StaticObjCreator _creator(pointee, std::forward<Args>(args)... );
        assert(pointee != nullptr);
    }
    static Type *getInstance() { return pointee.get(); }

    Type * operator->() { return &**this; }
    const Type* operator->() const { return &**this; }
    Type& operator *() { return *pointee; }
    const Type& operator *() const { return *pointee; }
private:
    static inline std::unique_ptr<Type> pointee = nullptr;
};

class ClassA {
public:
    ClassA() { std::cout << "ClassA::ClassA()" << std::endl; }
    ~ClassA() { std::cout << "ClassA::~ClassA()" << std::endl; }
    void foo() {
        std::cout << "ClassA::foo()" << std::endl;
    }
};

class ClassB {
public:
    ClassB(int, double, std::string) {}
    void foo() {}
    void bar() {}
};

int main()
{
    Singleton<ClassA> a; // -> can be instantiated like a normal class
    Singleton<ClassA> aa; // -> aa will be referenced to a
    Singleton<ClassB> b(1, 3.14, "hello world!"); // -> 
    a->foo();
    Singleton<ClassA>::getInstance()->foo();
    b->bar();
}

Merhaba, ClassA foo fonksiyonunda "}" eksik kalmış.

@makifay teşekkürler.