Removal of ACE_Singleton with some other Singleton class from BOOST or C++14 class

We are migrating from C++03 to C++14 and it is the decision to go way from ACE lib. We mostly use ACE lib for Singleton objects and locks. So for locks we can use mutex from C++11/14 but what would be the better replacement of ACE_SINGLETON.

Solution

#include <iostream>

class foo;

foo& get_foo();

class foo
{
    friend foo& get_foo();;
private:
    ~foo () { std::cout << "foo destroyed" << std::endl; }
    foo () { std::cout << "foo constructed" << std::endl; }
    foo(const foo&) = delete;
    foo& operator=(const foo&) = delete;
};

foo&
get_foo()
{
    static foo f;
    return f;
}

int
main()
{
    auto& f = get_foo();
}

If you are using Visual Studio, you need VS-2015 or later.

Thread-local statics have thread safe initialization in C++11 and forward.

Update

template <class T>
class Singleton
{
public:
    static T& getinstance()
    {
        static T t;
        return t;
    }
};

But in the final analysis, I'm a big fan of KISS. And there's nothing much simpler than writing a get_foo() factory function for your singleton (thanks to thread-safe function local statics). Since the language now supplies the hard part (thread safe initialization), class Singleton<T> adds little value imho.

Here is recent code I've written indicating that I practice what I'm saying:

https://github.com/HowardHinnant/date/blob/master/src/tz.cpp#L573-L578

In this particular case I needed to have a quite complicated construction process for my singleton, and even the ability to occasionally re-initialize it. But it still boiled down to a factory function wrapped around a function-local-static.