Add a niche to box

4 files changed, 27 insertions, 21 deletions

diff --git a/asl/annotations.hpp b/asl/annotations.hpp
index a398e13..fc65378 100644
--- a/asl/annotations.hpp
+++ b/asl/annotations.hpp
@@ -2,7 +2,6 @@
 

 #include "asl/config.hpp"

 

-

 #if ASL_COMPILER_CLANG_CL

     #define ASL_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]

 #elif ASL_COMPILER_CLANG

diff --git a/asl/box.hpp b/asl/box.hpp
index d8ccd36..7556d76 100644
--- a/asl/box.hpp
+++ b/asl/box.hpp
@@ -16,15 +16,18 @@ class box
     ASL_NO_UNIQUE_ADDRESS Allocator m_alloc;

     

 public:

-    explicit constexpr box(T* ptr = nullptr)

+    explicit constexpr box(niche)

         requires default_constructible<Allocator>

-        : m_ptr{ptr}

+        : m_ptr{nullptr}

+        , m_alloc{}

     {}

-    

+

     constexpr box(T* ptr, Allocator alloc)

         : m_ptr{ptr}

         , m_alloc{ASL_MOVE(alloc)}

-    {}

+    {

+        ASL_ASSERT(m_ptr != nullptr);

+    }

 

     constexpr box(box&& other)

         : m_ptr{exchange(other.m_ptr, nullptr)}

@@ -77,6 +80,11 @@ public:
         ASL_ASSERT(m_ptr != nullptr);

         return m_ptr;

     }

+

+    constexpr bool operator==(niche) const

+    {

+        return m_ptr == nullptr;

+    }

 };

 

 template<is_object T, allocator Allocator = DefaultAllocator, typename... Args>

diff --git a/asl/meta.hpp b/asl/meta.hpp
index f0397a1..72b36fd 100644
--- a/asl/meta.hpp
+++ b/asl/meta.hpp
@@ -160,4 +160,13 @@ template<typename T, int N> struct _is_array_helper<T[N]> : true_type  {};
 

 template<typename T> concept is_array = _is_array_helper<T>::value;

 

+struct niche {};

+

+template<typename T>

+concept has_niche = constructible_from<T, niche> &&

+    requires (const T& value, niche n)

+    {

+        { value == n } -> same_as<bool>;

+    };

+

 } // namespace asl

diff --git a/asl/tests/box_tests.cpp b/asl/tests/box_tests.cpp
index f1a35f3..3813639 100644
--- a/asl/tests/box_tests.cpp
+++ b/asl/tests/box_tests.cpp
@@ -4,30 +4,20 @@
 #include "asl/tests/test_types.hpp"

 

 static_assert(sizeof(asl::box<int>) == sizeof(int*));

-static_assert(asl::default_constructible<asl::box<int>>);

 static_assert(!asl::copyable<asl::box<int>>);

 static_assert(asl::moveable<asl::box<int>>);

-static_assert(asl::default_constructible<asl::box<NonMoveConstructible>>);

+static_assert(asl::has_niche<asl::box<int>>);

 

 ASL_TEST(destructor)

 {

     bool d = false;

 

     {

-        asl::box<DestructorObserver> box2;

-    

-        {

-            auto box = asl::make_box<DestructorObserver>(&d);

-            ASL_TEST_ASSERT(!d);

-    

-

-            auto box3 = ASL_MOVE(box);

-            ASL_TEST_ASSERT(!d);

-

-            box2 = ASL_MOVE(box3);

-            ASL_TEST_ASSERT(!d);

-        }

-    

+        auto box = asl::make_box<DestructorObserver>(&d);

+        ASL_TEST_ASSERT(!d);

+

+

+        auto box3 = ASL_MOVE(box);

         ASL_TEST_ASSERT(!d);

     }