Add various copy assignment operators to not_null and maybe_null_*.

Also removed unused constant member variable that seemed to be there
to prevent maybe_null_* being used with anything other than a pointer,
which is being taken care of with a static_assert now.

include/gsl.h

@@ -111,21 +111,27 @@ class not_null
     static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
 public:
     not_null(T t) : ptr_(t) { ensure_invariant(); }
-
-    // deleting these two prevents compilation when initialized with a nullptr or literal 0
-    not_null(std::nullptr_t) = delete;
-    not_null(int) = delete;
+    not_null& operator=(const T& t) { ptr_ = t; ensure_invariant(); return *this; }
 
     not_null(const not_null &other) = default;
+    not_null& operator=(const not_null &other) = default;
 
     template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    not_null(const not_null<U> &other) : ptr_(other.get())
+    not_null(const not_null<U> &other)
     {
+        *this = other;
     }
 
-    not_null<T>& operator=(const T& t) { ptr_ = t; ensure_invariant(); return *this; }
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    not_null& operator=(const not_null<U> &other)
+    {
+        ptr_ = other.get();
+        return *this;
+    }
 
     // prevents compilation when someone attempts to assign a nullptr 
+    not_null(std::nullptr_t) = delete;
+    not_null(int) = delete;
     not_null<T>& operator=(std::nullptr_t) = delete;
 	not_null<T>& operator=(int) = delete;
     
@@ -166,26 +172,18 @@ private:
 //
 // Describes an optional pointer - provides symmetry with not_null
 //
+template<class T>
+class maybe_null_ret;
+
 template<class T>
 class maybe_null_dbg
 {
     static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
 public:
     maybe_null_dbg() : ptr_(nullptr), tested_(false) {}
+    maybe_null_dbg(std::nullptr_t) : ptr_(nullptr), tested_(false) {}
 
     maybe_null_dbg(const T& p) : ptr_(p), tested_(false) {}
-    maybe_null_dbg(const maybe_null_dbg& rhs) : ptr_(rhs.ptr_), tested_(false) {}
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    maybe_null_dbg(const not_null<U> &other) : ptr_(other.get()), tested_(false)
-    {
-    }
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    maybe_null_dbg(const maybe_null_dbg<U> &other) : ptr_(other.get()), tested_(false)
-    {
-    }
-
     maybe_null_dbg& operator=(const T& p)
     {
         if (ptr_ != p)
@@ -196,6 +194,8 @@ public:
         return *this;
     }
 
+
+    maybe_null_dbg(const maybe_null_dbg& rhs) : ptr_(rhs.ptr_), tested_(false) {}
     maybe_null_dbg& operator=(const maybe_null_dbg& rhs)
     {
         if (this != &rhs)
@@ -206,6 +206,43 @@ public:
         return *this;
     }
 
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg(const not_null<U> &other) : ptr_(other.get()), tested_(false) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg& operator=(const not_null<U> &other)
+    {
+        ptr_ = other.get();
+        tested_ = false;
+        return *this;
+    }
+
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg(const maybe_null_dbg<U> &other) : ptr_(other.get()), tested_(false) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg& operator=(const maybe_null_dbg<U> &other)
+    {
+        ptr_ = other.get();
+        tested_ = false;
+        return *this;
+    }
+
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg(const maybe_null_ret<U> &other) : ptr_(other.get()), tested_(false) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_dbg& operator=(const maybe_null_ret<U> &other)
+    {
+        ptr_ = other.get();
+        tested_ = false;
+        return *this;
+    }
+
+
     bool present() const { tested_ = true; return ptr_ != nullptr; }
 
     bool operator==(const T& rhs) const { tested_ = true; return ptr_ == rhs; }
@@ -225,8 +262,6 @@ public:
     T operator->() const { return get(); }
 
 private:
-    const size_t ptee_size_ = sizeof(*ptr_);  // T must be a pointer type
-
     // unwanted operators...pointers only point to single objects!
     // TODO ensure all arithmetic ops on this type are unavailable
     maybe_null_dbg<T>& operator++() = delete;
@@ -249,27 +284,46 @@ class maybe_null_ret
 public:
     maybe_null_ret() : ptr_(nullptr) {}
     maybe_null_ret(std::nullptr_t) : ptr_(nullptr) {}
+
     maybe_null_ret(const T& p) : ptr_(p) {}
+    maybe_null_ret& operator=(const T& p) { ptr_ = p; return *this; }
+    
     maybe_null_ret(const maybe_null_ret& rhs) = default;
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    maybe_null_ret(const not_null<U> &other) : ptr_(other.get())
-    {
-    }
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    maybe_null_ret(const maybe_null_ret<U> &other) : ptr_(other.get())
-    {
-    }
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    maybe_null_ret(const maybe_null_dbg<U> &other) : ptr_(other.get())
-    {
-    }
-
-    maybe_null_ret& operator=(const T& p) { if (ptr_ != p) { ptr_ = p; } return *this; }
     maybe_null_ret& operator=(const maybe_null_ret& rhs) = default;
 
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret(const not_null<U> &other) : ptr_(other.get()) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret& operator=(const not_null<U> &other)
+    {
+        ptr_ = other.get();
+        return *this;
+    }
+
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret(const maybe_null_ret<U> &other) : ptr_(other.get()) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret& operator=(const maybe_null_ret<U> &other)
+    {
+        ptr_ = other.get();
+        return *this;
+    }
+
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret(const maybe_null_dbg<U> &other) : ptr_(other.get()) {}
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    maybe_null_ret& operator=(const maybe_null_dbg<U> &other)
+    {
+        ptr_ = other.get();
+        return *this;
+    }
+
+
     bool present() const { return ptr_ != nullptr; }
 
     T get() const { return ptr_; }
@@ -289,7 +343,6 @@ private:
     maybe_null_ret<T>& operator-(size_t) = delete;
     maybe_null_ret<T>& operator-=(size_t) = delete;
 
-    const size_t ptee_size_ = sizeof(*ptr_);  // T must be a pointer type
     T ptr_;
 };
 

tests/maybenull_tests.cpp

@@ -17,6 +17,7 @@
 #include <UnitTest++/UnitTest++.h> 
 #include <gsl.h>
 #include <vector>
+#include <iostream>
 
 using namespace Guide;
 
@@ -254,6 +255,43 @@ SUITE(MaybeNullTests)
         // Make sure we no longer throw here
         CHECK(p1.get() != nullptr);
     }
+
+    TEST(TestMaybeNullAssignmentOps)
+    {
+        MyBase base;
+        MyDerived derived;
+        Unrelated unrelated;
+
+        not_null<MyBase*> nnBase(&base);
+        not_null<MyDerived*> nnDerived(&derived);
+        not_null<Unrelated*> nnUnrelated(&unrelated);
+
+        maybe_null_ret<MyBase*> mnBase_ret1(&base), mnBase_ret2;
+        mnBase_ret2 = mnBase_ret1; // maybe_null_ret<T> = maybe_null_ret<T>
+        mnBase_ret2 = nnBase; // maybe_null_ret<T> = not_null<T>
+
+        maybe_null_ret<MyDerived*> mnDerived_ret(&derived);
+        mnBase_ret2 = mnDerived_ret; // maybe_null_ret<T> = maybe_null_ret<U>
+        mnBase_ret1 = &derived; // maybe_null_ret<T> = U;
+        mnBase_ret1 = nnDerived; // maybe_null_ret<T> = not_null<U>
+
+        maybe_null_ret<Unrelated*> mnUnrelated_ret;
+        mnUnrelated_ret = &unrelated; // maybe_null_ret<T> = T
+
+        maybe_null_dbg<MyBase*> mnBase_dbg1(&base), mnBase_dbg2;
+        mnBase_dbg2 = mnBase_dbg1; // maybe_null_dbg<T> = maybe_null_dbg<T>
+        mnBase_dbg2 = nnBase; // maybe_null_dbg<T> = not_null<T>
+
+        maybe_null_dbg<MyDerived*> mnDerived_dbg(&derived);
+        CHECK(mnDerived_dbg.present());
+        mnBase_dbg2 = mnDerived_dbg; // maybe_null_dbg<T> = maybe_null_dbg<U>
+        
+        mnBase_dbg1 = &derived; // maybe_null_dbg<T> = U;
+        mnBase_dbg1 = nnDerived; // maybe_null_dbg<T> = not_null<U>
+
+        maybe_null_dbg<Unrelated*> mnUnrelated_dbg;
+        mnUnrelated_dbg = &unrelated; // maybe_null_dbg<T> = T
+    }
 }
 
 int main(int, const char *[])

tests/notnull_tests.cpp

@@ -65,12 +65,19 @@ SUITE(NotNullTests)
 
     TEST(TestNotNullCasting)
     {
-        MyDerived derived;
+        MyBase base;
+	MyDerived derived;
+	Unrelated unrelated;
+	not_null<Unrelated*> u = &unrelated;
         not_null<MyDerived*> p = &derived;
-        not_null<MyBase*> q = p;
+        not_null<MyBase*> q = &base;
+	q = p; // allowed with heterogeneous copy ctor
         CHECK(q == p);
 
 #ifdef CONFIRM_COMPILATION_ERRORS
+	q = u; // no viable conversion possible between MyBase* and Unrelated*
+	p = q; // not possible to implicitly convert MyBase* to MyDerived*
+
         not_null<Unrelated*> r = p;
         not_null<Unrelated*> s = reinterpret_cast<Unrelated*>(p);
 #endif