C++17: Use std::invoke().

This makes code more generic. Maybe this will let us simplify code.

sigc++/adaptors/adaptor_trait.h

@@ -25,6 +25,7 @@
 #include <sigc++/functors/ptr_fun.h>
 #include <sigc++/functors/mem_fun.h>
 #include <sigc++/adaptors/adaptor_base.h>
+#include <functional>
 
 /*
  * The idea here is simple.  To prevent the need to
@@ -96,7 +97,7 @@ struct adaptor_functor : public adaptor_base
   template <typename... T_arg>
   decltype(auto) operator()(T_arg&&... arg) const
   {
-    return functor_(std::forward<T_arg>(arg)...);
+    return std::invoke(functor_, std::forward<T_arg>(arg)...);
   }
 
   /// Constructs an invalid functor.

sigc++/adaptors/bind.h

@@ -26,6 +26,7 @@
 #include <sigc++/tuple-utils/tuple_start.h>
 #include <sigc++/tuple-utils/tuple_end.h>
 #include <sigc++/tuple-utils/tuple_transform_each.h>
+#include <functional>
 
 
 namespace sigc

sigc++/adaptors/bind_return.h

@@ -49,6 +49,7 @@ struct bind_return_functor : public adapts<T_functor>
   template <typename... T_arg>
   inline typename unwrap_reference<T_return>::type operator()(T_arg... a)
   {
+    //TODO: Use std::invoke() here?
     this->functor_.template operator()<type_trait_pass_t<T_arg>...>(a...);
     return ret_value_.invoke();
   }
@@ -71,7 +72,7 @@ template <typename T_return, typename T_functor>
 typename unwrap_reference<T_return>::type
 bind_return_functor<T_return, T_functor>::operator()()
 {
-  this->functor_();
+  std::invoke(this->functor_);
   return ret_value_.invoke();
 }
 

sigc++/adaptors/compose.h

@@ -19,6 +19,7 @@
 #ifndef SIGC_ADAPTORS_COMPOSE_H
 #define SIGC_ADAPTORS_COMPOSE_H
 #include <sigc++/adaptors/adapts.h>
+#include <functional>
 
 namespace sigc
 {
@@ -61,12 +62,14 @@ namespace sigc
 template <typename T_setter, typename T_getter>
 struct compose1_functor : public adapts<T_setter>
 {
-  decltype(auto) operator()() { return this->functor_(get_()); }
+  decltype(auto) operator()() {
+    return std::invoke(this->functor_, get_());
+  }
 
   template <typename... T_arg>
   decltype(auto) operator()(T_arg&&... a)
   {
-    return this->functor_(get_(std::forward<T_arg>(a)...));
+    return std::invoke(this->functor_, get_(std::forward<T_arg>(a)...));
   }
 
   /** Constructs a compose1_functor object that combines the passed functors.
@@ -95,12 +98,14 @@ struct compose1_functor : public adapts<T_setter>
 template <typename T_setter, typename T_getter1, typename T_getter2>
 struct compose2_functor : public adapts<T_setter>
 {
-  decltype(auto) operator()() { return this->functor_(get1_(), get2_()); }
+  decltype(auto) operator()() {
+    return std::invoke(this->functor_, get1_(), get2_());
+  }
 
   template <typename... T_arg>
   decltype(auto) operator()(T_arg... a)
   {
-    return this->functor_(get1_(a...), get2_(a...));
+    return std::invoke(this->functor_, get1_(a...), get2_(a...));
   }
 
   /** Constructs a compose2_functor object that combines the passed functors.

sigc++/adaptors/exception_catch.h

@@ -80,7 +80,7 @@ struct exception_catch_functor : public adapts<T_functor>
   {
     try
     {
-      return this->functor_();
+      return std::invoke(this->functor_);
     }
     catch (...)
     {
@@ -93,6 +93,7 @@ struct exception_catch_functor : public adapts<T_functor>
   {
     try
     {
+      //TODO: Use std::invoke here?
       return this->functor_.template operator()<type_trait_pass_t<T_arg>...>(a...);
     }
     catch (...)

sigc++/adaptors/retype.h

@@ -82,6 +82,7 @@ struct retype_functor : public adapts<T_functor>
   template <typename... T_arg>
   decltype(auto) operator()(T_arg... a)
   {
+    //TODO: Use std::invoke() here?
     return this->functor_.template operator()<type_trait_take_t<T_type>...>(
       static_cast<T_type>(a)...);
   }

sigc++/adaptors/retype_return.h

@@ -41,6 +41,7 @@ struct retype_return_functor : public adapts<T_functor>
   template <typename... T_arg>
   inline T_return operator()(T_arg&&... a)
   {
+    //TODO: Use std::invoke() here?
     return T_return(this->functor_.template operator() < T_arg... > (std::forward<T_arg>(a)...));
   }
 
@@ -60,7 +61,7 @@ template <typename T_return, typename T_functor>
 T_return
 retype_return_functor<T_return, T_functor>::operator()()
 {
-  return T_return(this->functor_());
+  return T_return(std::invoke(this->functor_));
 }
 
 /** Adaptor that performs a C-style cast on the return value of a functor.
@@ -81,6 +82,7 @@ struct retype_return_functor<void, T_functor> : public adapts<T_functor>
   template <typename... T_arg>
   inline void operator()(T_arg... a)
   {
+    //TODO: Use std::invoke() here?
     this->functor_.template operator()<T_arg...>(a...);
   }
 
@@ -92,7 +94,7 @@ template <typename T_functor>
 void
 retype_return_functor<void, T_functor>::operator()()
 {
-  this->functor_();
+  std::invoke(this->functor_);
 }
 
 #ifndef DOXYGEN_SHOULD_SKIP_THIS

sigc++/adaptors/track_obj.h

@@ -83,7 +83,9 @@ class track_obj_functor : public adapts<T_functor>
   /** Invokes the wrapped functor.
    * @return The return value of the functor invocation.
    */
-  decltype(auto) operator()() { return this->functor_(); }
+  decltype(auto) operator()() {
+    return std::invoke(this->functor_);
+  }
 
   /** Invokes the wrapped functor passing on the arguments.
    * @param arg Arguments to be passed on to the functor.
@@ -92,6 +94,7 @@ class track_obj_functor : public adapts<T_functor>
   template <typename... T_arg>
   decltype(auto) operator()(T_arg&&... arg)
   {
+    //TODO: Use std::invoke() here?
     return this->functor_.template operator()<type_trait_pass_t<T_arg>...>(
       std::forward<T_arg>(arg)...);
   }

sigc++/functors/mem_fun.h

@@ -21,6 +21,7 @@
 #include <sigc++/type_traits.h>
 #include <sigc++/limit_reference.h>
 #include <sigc++/member_method_trait.h>
+#include <functional>
 
 // implementation notes:
 //  - we do not use bind here, because it would introduce
@@ -113,7 +114,7 @@ class mem_functor
    */
   decltype(auto) operator()(obj_type_with_modifier& obj, type_trait_take_t<T_arg>... a) const
   {
-    return (obj.*func_ptr_)(a...);
+    return std::invoke(func_ptr_, obj, a...);
   }
 
 protected:
@@ -152,7 +153,7 @@ class bound_mem_functor : mem_functor<T_func, T_arg...>
    */
   decltype(auto) operator()(type_trait_take_t<T_arg>... a) const
   {
-    return (obj_.invoke().*(this->func_ptr_))(a...);
+    return std::invoke(this->func_ptr_, obj_.invoke(), a...);
   }
 
   // protected:

sigc++/functors/ptr_fun.h

@@ -19,6 +19,7 @@
 #ifndef SIGC_FUNCTORS_PTR_FUN_H
 #define SIGC_FUNCTORS_PTR_FUN_H
 #include <sigc++/type_traits.h>
+#include <functional>
 
 namespace sigc
 {
@@ -92,7 +93,9 @@ class pointer_functor<T_return(T_args...)>
    * @param a Arguments to be passed on to the function.
    * @return The return value of the function invocation.
    */
-  T_return operator()(type_trait_take_t<T_args>... a) const { return func_ptr_(a...); }
+  T_return operator()(type_trait_take_t<T_args>... a) const {
+    return std::invoke(func_ptr_, a...);
+  }
 };
 
 /** Creates a functor of type sigc::pointer_functor which wraps an existing non-member function.

sigc++/functors/slot.h

@@ -23,6 +23,7 @@
 #include <sigc++/visit_each.h>
 #include <sigc++/adaptors/adaptor_trait.h>
 #include <sigc++/functors/slot_base.h>
+#include <functional>
 
 #include <memory>
 
@@ -190,8 +191,10 @@ class slot<T_return(T_arg...)> : public slot_base
    */
   inline T_return operator()(type_trait_take_t<T_arg>... a) const
   {
-    if (!empty() && !blocked())
-      return (reinterpret_cast<call_type>(slot_base::rep_->call_))(slot_base::rep_, a...);
+    if (!empty() && !blocked()) {
+      return std::invoke(reinterpret_cast<call_type>(slot_base::rep_->call_), slot_base::rep_, a...);
+    }
+
     return T_return();
   }
 

sigc++/visit_each.h

@@ -21,6 +21,7 @@
 #include <sigc++/type_traits.h>
 #include <type_traits>
 #include <utility> // std::forward
+#include <functional>
 
 namespace sigc
 {
@@ -45,7 +46,7 @@ struct limit_trackable_target
   {
     //Only call action_() if T_Type derives from trackable.
     if constexpr(is_base_of_or_same_v<sigc::trackable, T_type>) {
-        action_(type);
+        std::invoke(action_, type);
     }
   }