meta: minor changes to invoke

include/utl/meta/invoke.h

@@ -66,14 +66,13 @@ namespace meta{
    template <typename _Tp>
    struct identity {
    #if defined (UTL_WORKAROUND_CWG_1558)
-      // decltype via use_() using Ts... to set the apply type
+      // redirect unused Ts... via void_t
       template <typename... Ts>
-      using _dummy = void_t<Ts...>;
-      using apply = _Tp;   //!< identity is invokable, must also have apply
+      using apply = first_of<_Tp, void_t<Ts...>>;   //!< identity is invokable, must also have apply
    #else
       template <typename...>
       using apply = _Tp;   //!< identity is invokable, must also have apply
-   #endif
+#endif
       using type = _Tp;    //!< identity
    };
 
@@ -82,40 +81,68 @@ namespace meta{
    using identity_t = type_<identity<_Tp>>;
    //! @}
 
-   //! Is evaluable trait
+   //! Is applicable trait
    //! @{
    namespace detail {
 
-      // we check for template \p F to be a metafunction with parameters \p T
       template<template<typename...> class F, typename... T>
-      struct is_evaluable_ {
+      struct is_applicable_ {
          template<template<typename...> class G, typename = G<T...>>
-            static true_ check (int);
+            static true_ check (int);  //< T.. can be passed to G
          template<template<typename...> class>
-            static false_ check (...);
+            static false_ check (...); //< all other combinations
 
          using type = decltype(check<F>(0));
       };
 
-      // we check for template \p F with integral constant parameters \p Is of type \p T
-//      template<typename T, template <T...> class F, T... Is>
-//      struct is_evaluable_i_ {
-//         template<typename TT, template <TT...> class G, class = G<Is...>>
-//            static true_ check (int);
-//         template<typename, template<typename...> class>
-//            static false_ check (...);
-//
-//         using type = decltype(check<T, F>(0));
-//      };
+      template <typename Fn, typename... Args>
+      using use_ = typename Fn::template apply<Args...>;
+
+      template<typename F, typename... T>
+      struct is_applicable_q_ {
+         template<typename G, typename Ret= type_<use_<G, T...>>>
+            static Ret check (int);  //< T.. can be passed to G
+         template<typename...>
+            static nil_ check (...); //< all other combinations
+
+         using type = decltype(check<F>(0));
+      };
+
+      template<typename T, template <T...> class F, T... Is>
+      struct is_applicable_i_ {
+         template<typename TT, template<TT...> class G, typename =G<Is...>>
+            static true_ check (int);  //< Is... can be passed to G
+         template<typename TT, template<TT...> class G>
+            static false_ check (...); //< all other combinations
+
+         using type = decltype(check<T, F>(0));
+      };
    }
 
+   //! check if we can instantiate \p F with parameters \p T
    template<template<typename...> class F, typename... T>
-   using is_evaluable = type_<
-         detail::is_evaluable_<F, T...>
+   using is_applicable_t = type_<
+         detail::is_applicable_<F, T...>
+   >;
+   //! check if we can instantiate \p Q with parameters \p T and the instant
+   //! is different from \c nil_
+   template<typename Q, typename... T>
+   using is_applicable_qt = type_ <
+      // Extra check for quoted metafunctions to check return type
+      if_ <
+         not_same_<
+            type_ <detail::is_applicable_q_ <Q, T...>>,
+            nil_
+         >,
+         true_,
+         false_
+      >
+   >;
+   //! check if we can instantiate \p F with parameters \p Is of type \p T
+   template <typename T, template<T...> class F, T... Is>
+   using is_applicable_it = type_<
+         detail::is_applicable_i_<T, F, Is...>
    >;
-
-//   template <typename T, template<T...> class F, T... Is>
-//   using is_evaluable_i = type_<detail::is_evaluable_i_<T, F<Is...>>>;
 
    //! @}
 
@@ -128,11 +155,12 @@ namespace meta{
          using type = F<Ts...>;
       };
 
-//      template<typename T, template<T...> class F, T... Is>
-//      struct defer_i_ {
-//         using type = F<Is...>;
-//      };
-      //!
+      template<typename T, template<T...> class F, T... Is>
+      struct defer_i_ {
+         using type = F<Is...>;
+      };
+
+      //! \note
       //! We use struct instead of:
       //! template<template<typename...> class F, typename... Ts>
       //! using defer_ =  F<Ts...>;
@@ -150,18 +178,18 @@ namespace meta{
    //! defer alias template for F<Ts...>
    template<template<class...> class F, class... Ts>
    using defer = if_<
-         is_evaluable<F, Ts...>,
+         detail::is_applicable_<F, Ts...>,
          detail::defer_<F, Ts...>,
-         nil_
+         nil_  //!< This should be identity<nil_> if nil_ was empty
    >;
 
    //! defer_i alias template for F<T, Is...>
-//   template <typename T, template<T...> class F, T... Is>
-//   using defer_i = if_ <
-//         is_evaluable_i<T, F<Is...>>,
-//         detail::defer_i_<F, Is...>,
-//         nil_
-//   >;
+   template <typename T, template<T...> class F, T... Is>
+   using defer_i = if_ <
+         detail::is_applicable_i_<T, F, Is...>,
+         detail::defer_i_<T, F, Is...>,
+         nil_  //!< This should be identity<nil_> if nil_ was empty
+   >;
    //! @}
 
    /*!
@@ -171,27 +199,35 @@ namespace meta{
    template <template <typename...> class F>
    struct quote {
       template <typename... Args>
-      using apply = type_<defer<F, Args...>>;   //!< defer here to avoid DR1430
+      using apply = type_<
+            defer<F, Args...>    //!< defer here to avoid DR1430
+      >;
    };
 
    //! Wrap a template \p F taking literals of type \p T into an Invokable
-//   template <typename T, template <T...> class F>
-//   struct quote_i {
-//      // requires meta::Integral
-//      template <typename... Is>
-//      using apply = type_<
-//            defer_i<T, F, Is...>  //!< defer here to avoid DR1430
-//      >;
-//   };
+   template <typename T, template <T...> class F>
+   struct quote_i {
+      // requires meta::Integral
+      template <typename... Ts>
+      using apply = type_<
+            defer_i<T, F, Ts::type::value...>  //!< defer here to avoid DR1430
+      >;
+   };
 
    /*!
     * Invoke the nested apply metafunction from \c Fn
     * with the arguments \c Args.
-    * requires Invocable(Fn)
     */
    template <typename Fn, typename... Args>
    using invoke = typename Fn::template apply<Args...>;
 
+   /*!
+    * Invoke the nested apply metafunction from \c Fn
+    * with the arguments \c Args.
+    */
+   template <typename Fn, typename... Args>
+   using invoke_t = type_<invoke <Fn, Args...>>;
+
    //! compose
    //! @{
    namespace detail {
@@ -214,34 +250,64 @@ namespace meta{
          using apply = invoke<Fn0, Args...>;
       };
    }
+
    /*!
-    * Create an invokable from other invokables by composition
-    * ex:
-    *    compose<Fns...> will result to something like F0<F1<F2<F3<...>>>>
+    * Create an invokable from other invocables by composition.
+    * \note
+    *    This implies from N invocables in \p Fns the first N-1 has to be unary.
+    *    That because of the "return" type of metafunction. They can only return one
+    *    type. So for n-ary invocables in the N-1 places the typelist<> is the solution.
+    * \example
+    * \code
+    *    static_assert(std::is_same<
+    *          invoke<compose<F1, F2, F3>, int>,
+    *          F1 <F2 <F3 <int>>>
+    *    >, "" );
+    * \endcode
     */
    template <typename... Fns>
    using compose = detail::compose_<Fns...>;
    //! @}
 
-   //! Applies the Invocable \p Fn by binding the arguments \p Ts
-   //! to the \e front of \p Fn.
+   /*!
+    * Applies the Invocable \p Fn by binding the arguments \p Ts
+    * to the front of \p Fn.
+    */
    template<typename Fn, typename... Ts>
    struct bind_front {
        template<typename... Us>
        using apply = invoke<Fn, Ts..., Us...>;
    };
 
-   //! Applies the Invocable \p Fn by binding the arguments \p Ts
-   //! to the \e back of \p Fn.
+   /*!
+    * Applies the Invocable \p Fn by binding the arguments \p Ts
+    * to the back of \p Fn.
+    */
    template<typename Fn, typename... Ts>
    struct bind_back {
        template<typename... Us>
        using apply = invoke<Fn, Us..., Ts...>;
    };
 
+   /*
+    * ========== predicates ============
+    */
+   template <typename T1>
+   struct same_as {
+      template < typename T2>
+      struct apply : same_<T1, T2> { };
+   };
+
+   template <typename T1>
+   struct not_same_as {
+      template < typename T2>
+      struct apply : not_same_<T1, T2> { };
+   };
+
+
    //! @}
 }}
 
 //! @}
 
-#endif /* __utl_meta_utility_h__ */
+#endif /* __utl_meta_invoke_h__ */