examples

commit c00d0b4d3c6d0a3eed86310c265f620c4a883264
parent 5f86adcc15715188678dcda4bcca1e09de7f32f7
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Fri, 22 Sep 2023 21:21:01 +0100

type-erased-unique_ptr: Add example of type erasure

Diffstat:
A
src/type-erased-unique_ptr.cpp
 | 
80
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 80 insertions(+), 0 deletions(-)
diff --git a/src/type-erased-unique_ptr.cpp b/src/type-erased-unique_ptr.cpp
@@ -0,0 +1,79 @@
+#include <utility>
+#include <iostream>
+
+template <typename T = void>
+struct unique_ptr
+{
+    unique_ptr() = default;
+    explicit unique_ptr(T* p)
+    :   p(p)
+    {}
+    ~unique_ptr() { if (p) delete p; }
+    unique_ptr(unique_ptr&& old)
+    :   p{std::exchange(old.p, nullptr)}
+    {}
+    unique_ptr& operator =(unique_ptr&& old)
+    {
+        if (p)
+            delete p;
+        p = std::exchange(old.p, nullptr);
+        return *this;
+    }
+private:
+    T* p = nullptr;
+
+    friend struct unique_ptr<void>;
+};
+
+template<>
+struct unique_ptr<void>
+{
+    unique_ptr() = default;
+
+    ~unique_ptr()
+    {
+        if (p)
+            d(p);
+    }
+
+    unique_ptr(unique_ptr&& old)
+    :   p{std::exchange(old.p, nullptr)}
+    ,   d{std::exchange(old.d, nullptr)}
+    {}
+
+    unique_ptr& operator =(unique_ptr&& old)
+    {
+        if (p)
+            d(p);
+        p = std::exchange(old.p, nullptr);
+        d = std::exchange(old.d, nullptr);
+        return *this;
+    }
+
+    template <typename T>
+    unique_ptr(unique_ptr<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()
+{
+    unique_ptr<> s2;
+    {
+        unique_ptr<sentry> s1{new sentry};
+        s2 = std::move(s1);
+        std::cout << "~s1\n";
+    }
+    std::cout << "~s2\n";
+}
+\ No newline at end of file