examples

commit a67325eb6c28db74bb43e9197ba5eaa4afb3faf9
parent 8d22581197d69a18816496fb3693e16b8f04b350
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Fri, 14 Jul 2023 22:55:37 +0100

template-specialisation: Example showing type-erased unique pointer

Diffstat:
A
src/template_specialisation.cpp
 | 
87
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 87 insertions(+), 0 deletions(-)
diff --git a/src/template_specialisation.cpp b/src/template_specialisation.cpp
@@ -0,0 +1,87 @@
+#include <utility>
+#include <memory>
+#include <iostream>
+
+template <typename T = void>
+struct S
+{
+	S() = default;
+
+	explicit S(T* p)
+	:   p(p)
+	{}
+
+	~S()
+	{
+		if (p)
+			delete p;
+	}
+		S(S&& old)
+	:	p{std::exchange(old.p, nullptr)}
+	{}
+
+	S& operator =(S&& old)
+	{
+		if (p)
+			delete p;
+		p = std::exchange(old.p, nullptr);
+		return *this;
+	}
+private:
+	T* p = nullptr;
+
+	friend struct S<void>;
+};
+
+template<>
+struct S<void>
+{
+	S() = default;
+
+	~S()
+	{
+		if (p)
+			d(p);
+	}
+
+	S(S&& old)
+	:	p{std::exchange(old.p, nullptr)}
+	,	d{std::exchange(old.d, nullptr)}
+	{}
+
+	S& operator =(S&& old)
+	{
+		if (p)
+			d(p);
+		p = std::exchange(old.p, nullptr);
+		d = std::exchange(old.d, nullptr);
+		return *this;
+	}
+
+	template <typename T>
+	S(S<T>&& old)
+	:	p{std::exchange(old.p, nullptr)}
+	,	d{[](void* x) { delete (T*)x; }}
+	{}
+
+private:
+	void* p = nullptr;
+	void (*d)(void*) = nullptr;
+};
+
+struct sentry
+{
+	sentry() { std::cout << __PRETTY_FUNCTION__ << std::endl; }
+	~sentry() { std::cout << __PRETTY_FUNCTION__ << std::endl; }
+};
+
+int main()
+{
+	S<> s2;
+	{
+		S<sentry> s1{new sentry};
+		s2 = std::move(s1);
+		std::cout << "~s1\n";
+	}
+	std::cout << "~s2\n";
+}