Remake deref

2 files changed, 31 insertions, 22 deletions

diff --git a/asl/base/meta.hpp b/asl/base/meta.hpp
index 06c7c59..8376d5c 100644
--- a/asl/base/meta.hpp
+++ b/asl/base/meta.hpp
@@ -90,6 +90,9 @@ template<typename T> concept moveable = move_constructible<T> && move_assignable
 template<typename To, typename From>
 concept convertible_from = __is_convertible(From, To);
 
+template<typename From, typename To>
+concept convertible_to = __is_convertible(From, To);
+
 template<typename Derived, class Base>
 concept derived_from = __is_class(Derived) && __is_class(Base) && convertible_from<const volatile Base*, const volatile Derived*>;
 
@@ -244,29 +247,28 @@ concept has_niche = constructible_from<T, niche_t> && equality_comparable_with<T
 template<typename T>
 concept is_niche = same_as<un_cvref_t<T>, niche_t>;
 
-template<typename T, typename U>
-concept _derefs_with_indirection_as = requires(T& t)
+template<typename From, typename To>
+concept _dereferenceable_as_convertible = requires(From& t)
 {
-    *t;
-    requires convertible_from<U&, decltype(*t)>;
+    { *t } -> convertible_to<To&>;
 };
 
-template<typename T, typename U>
-concept _derefs_reference_as = is_ref<T> && convertible_from<U&, T>;
-
-template<typename T, typename U>
-concept _derefs_value_as = !is_ref<T> && convertible_from<U&, T&>;
-
-template<typename U, _derefs_with_indirection_as<U> T>
-constexpr U& deref(T&& t) { return static_cast<U&>(*t); }
-
-template<typename U, _derefs_reference_as<U> T>
-constexpr U& deref(T&& t) { return static_cast<U&>(t); }
-
-template<typename U, _derefs_value_as<U> T>
-constexpr U& deref(T&& t) { return static_cast<U&>(t); }
+template<typename From, typename To>
+concept derefs_as = is_object<To> &&
+    (convertible_to<un_ref_t<From>&, To&> || _dereferenceable_as_convertible<un_ref_t<From>, To>);
 
-template<typename T, typename U>
-concept derefs_as = _derefs_with_indirection_as<T, U> || _derefs_reference_as<T, U> || _derefs_value_as<T, U>;
+template<typename To, derefs_as<To> From>
+constexpr auto&& deref(From&& from) // NOLINT(*forward*)
+{
+    if constexpr (_dereferenceable_as_convertible<From, To>)
+    {
+        using deref_type = decltype(*declval<From&&>());
+        return static_cast<copy_cref_t<deref_type, To>>(*static_cast<From&&>(from));
+    }
+    else
+    {
+        return static_cast<copy_cref_t<From&&, To>>(from);
+    }
+}
 
 } // namespace asl
diff --git a/asl/base/meta_tests.cpp b/asl/base/meta_tests.cpp
index 774f9bc..6c8efab 100644
--- a/asl/base/meta_tests.cpp
+++ b/asl/base/meta_tests.cpp
@@ -255,16 +255,22 @@ static_assert(asl::is_enum<Enum2>);
 
 static_assert(asl::derefs_as<int, int>);
 static_assert(asl::derefs_as<int*, int>);
+static_assert(!asl::derefs_as<const int*, int>);
 static_assert(asl::derefs_as<int&, int>);
+static_assert(!asl::derefs_as<const int&, int>);
 static_assert(asl::derefs_as<asl::box<int>, int>);
 
 static_assert(asl::derefs_as<Derived, Base>);
+static_assert(!asl::derefs_as<Base, Derived>);
 static_assert(asl::derefs_as<Derived*, Base>);
 static_assert(asl::derefs_as<Derived&, Base>);
+static_assert(!asl::derefs_as<Base&, Derived>);
 static_assert(asl::derefs_as<asl::box<Derived>, Base>);
+static_assert(asl::derefs_as<asl::box<Derived>, Derived>);
+static_assert(asl::derefs_as<asl::box<Base>, Base>);
 
 static void wants_int(int) {}
-static void wants_base(Base&) {}
+static void wants_base(const Base&) {}
 static void wants_base_ptr(Base*) {}
 
 ASL_TEST(deref)
@@ -285,10 +291,11 @@ ASL_TEST(deref)
     wants_base(asl::deref<Base>(&c));
     wants_base(asl::deref<Base>(d));
 
-    wants_base_ptr(&asl::deref<Base>(Derived{}));
     wants_base_ptr(&asl::deref<Base>(c));
     wants_base_ptr(&asl::deref<Base>(&c));
     wants_base_ptr(&asl::deref<Base>(d));
+
+    wants_base(asl::deref<Base>(std::move(d)));
 }
 
 static_assert(asl::same_as<asl::copy_cref_t<int, float>, float>);