A custom implementation of the Singleton design pattern, adapted to zero-cost CRTP architectures! I'm posting it here in case anyone finds the idea interesting :)
A small disclaimer: I'm just showing the work I'm proud of; I don't claim to have reinvented the Singleton because, let's face it, there's not really much to reinvent ;)
int main() {
World::instance().foo(); // ✓
World instance; // ✗
World::foo() // ✗
}// Copyright (c) December 2025 Félix-Olivier Dumas. All rights reserved.
// Licensed under the terms described in the LICENSE file
template<typename Derived>
struct Singleton {
public:
static Derived& instance() {
static Derived instance(Token{});
return instance;
}
protected:
struct Token {};
Singleton() = default;
private:
Singleton(const Singleton&) = delete;
Singleton& operator=(const Singleton&) = delete;
Singleton(Singleton&&) = delete;
Singleton& operator=(Singleton&&) = delete;
};
struct World final : Singleton<World> {
friend Singleton<World>;
void foo() const noexcept {}
private:
explicit World(Token) {}
};