function_traits: drop unused pieces

is_callable won't ever be needed because std::is_invokable is here; arg_number and returns() didn't find its users; and function_type has been just broken all along for member functions.

2 files changed, 6 insertions, 54 deletions

diff --git a/lib/util.cpp b/lib/util.cpp
index cc18d9ab..041a8aba 100644
--- a/lib/util.cpp
+++ b/lib/util.cpp
@@ -141,63 +141,29 @@ int f();
 static_assert(std::is_same<fn_return_t<decltype(f)>, int>::value,
               "Test fn_return_t<>");
 
-void f1(int);
-static_assert(function_traits<decltype(f1)>::arg_number == 1,
-              "Test fn_arg_number");
-
-void f2(int, QString);
-static_assert(std::is_same<fn_arg_t<decltype(f2), 1>, QString>::value,
+void f1(int, QString);
+static_assert(std::is_same<fn_arg_t<decltype(f1), 1>, QString>::value,
               "Test fn_arg_t<>");
 
-struct S {
-    int mf();
-};
-static_assert(is_callable_v<decltype(&S::mf)>, "Test member function");
-static_assert(returns<int, decltype(&S::mf)>(),
-              "Test returns<> with member function");
-
 struct Fo {
     int operator()();
 };
-static_assert(is_callable_v<Fo>, "Test is_callable<> with function object");
-static_assert(function_traits<Fo>::arg_number == 0, "Test function object");
 static_assert(std::is_same<fn_return_t<Fo>, int>::value,
               "Test return type of function object");
 
 struct Fo1 {
     void operator()(int);
 };
-static_assert(function_traits<Fo1>::arg_number == 1, "Test function object 1");
-static_assert(is_callable_v<Fo1>, "Test is_callable<> with function object 1");
 static_assert(std::is_same<fn_arg_t<Fo1>, int>(),
               "Test fn_arg_t defaulting to first argument");
 
 #if (!defined(_MSC_VER) || _MSC_VER >= 1910)
 static auto l = [] { return 1; };
-static_assert(is_callable_v<decltype(l)>, "Test is_callable_v<> with lambda");
 static_assert(std::is_same<fn_return_t<decltype(l)>, int>::value,
               "Test fn_return_t<> with lambda");
 #endif
 
 template <typename T>
-struct fn_object {
-    static int smf(double) { return 0; }
-};
-template <>
-struct fn_object<QString> {
-    void operator()(QString);
-};
-static_assert(is_callable_v<fn_object<QString>>, "Test function object");
-static_assert(returns<void, fn_object<QString>>(),
-              "Test returns<> with function object");
-static_assert(!is_callable_v<fn_object<int>>, "Test non-function object");
-// FIXME: These two don't work
-// static_assert(is_callable_v<decltype(&fn_object<int>::smf)>,
-//              "Test static member function");
-// static_assert(returns<int, decltype(&fn_object<int>::smf)>(),
-//              "Test returns<> with static member function");
-
-template <typename T>
 QString ft(T&&)
 {
     return {};
diff --git a/lib/util.h b/lib/util.h
index 788ce5bc..4631570f 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -154,23 +154,19 @@ struct function_traits : public _impl::fn_traits<void, T> {};
 // Specialisation for a function
 template <typename ReturnT, typename... ArgTs>
 struct function_traits<ReturnT(ArgTs...)> {
-    static constexpr auto is_callable = true;
     using return_type = ReturnT;
     using arg_types = std::tuple<ArgTs...>;
-    using function_type = std::function<ReturnT(ArgTs...)>;
-    static constexpr auto arg_number = std::tuple_size<arg_types>::value;
 };
 
 namespace _impl {
     template <typename AlwaysVoid, typename T>
-    struct fn_traits {
-        static constexpr auto is_callable = false;
-    };
+    struct fn_traits;
 
+    // Specialisation for function objects with (non-overloaded) operator()
+    // (this includes non-generic lambdas)
     template <typename T>
     struct fn_traits<decltype(void(&T::operator())), T>
-        : public fn_traits<void, decltype(&T::operator())> {
-    }; // A generic function object that has (non-overloaded) operator()
+        : public fn_traits<void, decltype(&T::operator())> {};
 
     // Specialisation for a member function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
@@ -190,16 +186,6 @@ template <typename FnT, int ArgN = 0>
 using fn_arg_t =
     std::tuple_element_t<ArgN, typename function_traits<FnT>::arg_types>;
 
-template <typename R, typename FnT>
-constexpr bool returns()
-{
-    return std::is_same<fn_return_t<FnT>, R>::value;
-}
-
-// Poor-man's is_invokable
-template <typename T>
-constexpr auto is_callable_v = function_traits<T>::is_callable;
-
 inline auto operator"" _ls(const char* s, std::size_t size)
 {
     return QLatin1String(s, int(size));