cetl::pf17::overloaded → cetl::overloaded (#131)

See issue #130

cetlvast/suites/unittest/test_pf17_variant_other.cpp

@@ -8,6 +8,7 @@
 // CSpell: words chronomorphize
 
 #include <cetl/pf17/variant.hpp>  // The tested header always goes first.
+#include <cetl/visit_helpers.hpp>
 #include "test_pf17_variant.hpp"
 #include <cetlvast/helpers.hpp>
 
@@ -675,7 +676,7 @@ TEST(test_variant, basic_operations)
     using cetl::pf17::holds_alternative;
     using cetl::pf17::get;
     using cetl::pf17::get_if;
-    using cetl::pf17::make_overloaded;
+    using cetl::make_overloaded;
     using cetl::pf17::in_place_index;
 
     variant<int, char, monostate> var;
@@ -818,7 +819,7 @@ TEST(test_variant, visit)
     using cetl::pf17::get;
     using cetl::pf17::visit;
     using cetl::pf17::monostate;
-    using cetl::pf17::make_overloaded;
+    using cetl::make_overloaded;
 #if __cpp_exceptions
     using cetl::pf17::bad_variant_access;
 #endif
@@ -898,7 +899,7 @@ TEST(test_variant, visit)
 
     // Constexpr visitation is not possible in C++14.
 #if __cplusplus >= 201703L
-    using cetl::pf17::make_overloaded;
+    using cetl::make_overloaded;
     using cetl::pf17::in_place_type;
     static_assert(1110 == visit(make_overloaded([](const std::int8_t a,
                                                    const float       b) { return a + static_cast<std::int64_t>(b); },

include/cetl/pf17/utility.hpp

@@ -55,54 +55,6 @@ constexpr in_place_index_t<I> in_place_index{};
 
 // --------------------------------------------------------------------------------------------
 
-/// This is a helper for use with \ref visit that uses standard overload resolution to pick the best overload
-/// among a set of lambdas given by the user. Unfortunately, in C++14 we have to use it with a factory function;
-/// please see \ref make_overloaded for details. In C++17 this can be used without the factory in a much simpler way.
-///
-/// This function is not found in the C++ standard library, but is a common extension in the wild.
-template <typename...>
-struct overloaded;
-template <typename T>
-struct overloaded<T> : public T
-{
-    using T::operator();
-    // SFINAE is needed to ensure this constructor does not hide the copy/move constructors.
-    template <typename A, std::enable_if_t<!std::is_same<overloaded<T>, std::decay_t<A>>::value, int> = 0>
-    constexpr explicit overloaded(A&& arg)
-        : T(std::forward<A>(arg))
-    {
-    }
-};
-template <typename T, typename... Ts>
-struct overloaded<T, Ts...> : public T, public overloaded<Ts...>
-{
-    using T::operator();
-    using overloaded<Ts...>::operator();
-    // If B were empty, the ctor would need sfinae to avoid hiding the copy/move ctors; ensure this is not so.
-    template <typename A, typename... B, std::enable_if_t<(sizeof...(B) > 0), int> = 0>
-    constexpr explicit overloaded(A&& a, B&&... b)
-        : T(std::forward<A>(a))
-        , overloaded<B...>(std::forward<B>(b)...)
-    {
-    }
-};
-
-/// Returns an instance of \ref overloaded that can be used with \ref visit. The usage is as follows:
-/// @code
-/// visit(make_overloaded(
-///     [](const auto&)        { return "fallback"; },
-///     [](double)             { return "double";   },
-///     [](const std::string&) { return "string";   }
-/// ), variant);
-/// @endcode
-template <typename... Ts>
-constexpr overloaded<Ts...> make_overloaded(Ts&&... ts)
-{
-    return overloaded<Ts...>(std::forward<Ts>(ts)...);
-}
-
-// --------------------------------------------------------------------------------------------
-
 // Non-standard extensions for internal use.
 // We keep the definitions here to make it clear they are designed to detect the above-defined types, not std:: ones.
 namespace detail

include/cetl/visit_helpers.hpp

@@ -0,0 +1,64 @@
+/// @file
+/// Contains helpers for building visitors for the `cetl::visit` invocation.
+///
+/// @copyright
+/// Copyright (C) OpenCyphal Development Team  <opencyphal.org>
+/// Copyright Amazon.com Inc. or its affiliates.
+/// SPDX-License-Identifier: MIT
+
+#ifndef CETL_VISIT_HELPERS_HPP_INCLUDED
+#define CETL_VISIT_HELPERS_HPP_INCLUDED
+
+#include <type_traits>
+
+namespace cetl
+{
+/// This is a helper for use with \ref visit that uses standard overload resolution to pick the best overload
+/// among a set of lambdas given by the user. Unfortunately, in C++14 we have to use it with a factory function;
+/// please see \ref make_overloaded for details. In C++17 this can be used without the factory in a much simpler way.
+///
+/// This function is not found in the C++ standard library, but is a common extension in the wild.
+template <typename...>
+struct overloaded;
+template <typename T>
+struct overloaded<T> : public T
+{
+    using T::operator();
+    // SFINAE is needed to ensure this constructor does not hide the copy/move constructors.
+    template <typename A, std::enable_if_t<!std::is_same<overloaded<T>, std::decay_t<A>>::value, int> = 0>
+    constexpr explicit overloaded(A&& arg)
+        : T(std::forward<A>(arg))
+    {
+    }
+};
+template <typename T, typename... Ts>
+struct overloaded<T, Ts...> : public T, public overloaded<Ts...>
+{
+    using T::operator();
+    using overloaded<Ts...>::operator();
+    // If B were empty, the ctor would need sfinae to avoid hiding the copy/move ctors; ensure this is not so.
+    template <typename A, typename... B, std::enable_if_t<(sizeof...(B) > 0), int> = 0>
+    constexpr explicit overloaded(A&& a, B&&... b)
+        : T(std::forward<A>(a))
+        , overloaded<B...>(std::forward<B>(b)...)
+    {
+    }
+};
+
+/// Returns an instance of \ref overloaded that can be used with \ref visit. The usage is as follows:
+/// @code
+/// visit(make_overloaded(
+///     [](const auto&)        { return "fallback"; },
+///     [](double)             { return "double";   },
+///     [](const std::string&) { return "string";   }
+/// ), variant);
+/// @endcode
+template <typename... Ts>
+constexpr overloaded<Ts...> make_overloaded(Ts&&... ts)
+{
+    return overloaded<Ts...>(std::forward<Ts>(ts)...);
+}
+
+}  // namespace cetl
+
+#endif  // CETL_VISIT_HELPERS_HPP_INCLUDED