Document operator->*

doc/lambda2/reference.adoc

@@ -86,6 +86,10 @@ template<class A, class B> auto operator^=( A && a, B && b );
 template<class A, class B> auto operator<<=( A && a, B && b );
 template<class A, class B> auto operator>>=( A && a, B && b );
 
+// additional binary operators
+
+template<class A, class B> auto operator->*( A && a, B && b );
+
 } // namespace lambda2
 } // namespace boost
 ```
@@ -388,3 +392,16 @@ template<class A, class B> auto operator@=( A && a, B && b );
 +
 Returns: :: `std::bind( fn, std::forward<A>(a), std::forward<B>(b) );`,
   where `fn` is a function object such that `fn(x, y)` returns `x @= y`.
+
+### Additional Binary Operators
+
+```
+template<class A, class B> auto operator->*( A && a, B && b );
+```
+[none]
+* {blank}
++
+Returns: :: `std::bind( std::forward<B>(b), std::forward<A>(a) );`
+Notes: :: This operator is intended to be used with "projection" function
+  objects such as member pointers or member functions taking zero arguments,
+  as in `_1\->*&X::m` or `_1\->*&X::f`.

include/boost/lambda2/lambda2.hpp

@@ -232,7 +232,7 @@ template<class A, class = std::enable_if_t<!lambda2_detail::is_stream<A>::value>
     class B, class = lambda2_detail::enable_binary_lambda<A, B>>
 auto operator<<( A&& a, B&& b )
 {
-    return std::bind( lambda2_detail::left_shift(), std::forward<A>(a), std::forward<B>(b) ); \
+    return std::bind( lambda2_detail::left_shift(), std::forward<A>(a), std::forward<B>(b) );
 }
 
 template<class A, class = std::enable_if_t<lambda2_detail::is_stream<A>::value>,
@@ -248,7 +248,7 @@ template<class A, class = std::enable_if_t<!lambda2_detail::is_stream<A>::value>
     class B, class = lambda2_detail::enable_binary_lambda<A, B>>
 auto operator>>( A&& a, B&& b )
 {
-    return std::bind( lambda2_detail::right_shift(), std::forward<A>(a), std::forward<B>(b) ); \
+    return std::bind( lambda2_detail::right_shift(), std::forward<A>(a), std::forward<B>(b) );
 }
 
 template<class A, class = std::enable_if_t<lambda2_detail::is_stream<A>::value>,
@@ -258,6 +258,14 @@ auto operator>>( A& a, B&& b )
     return std::bind( lambda2_detail::right_shift(), std::ref(a), std::forward<B>(b) );
 }
 
+// operator->*
+
+template<class A, class B, class = lambda2_detail::enable_unary_lambda<A>>
+auto operator->*( A&& a, B&& b )
+{
+    return std::bind( std::forward<B>(b), std::forward<A>(a) );
+}
+
 } // namespace lambda2
 } // namespace boost
 

test/Jamfile

@@ -26,3 +26,4 @@ run subscript.cpp ;
 run compound.cpp ;
 run stream_insert.cpp ;
 run stream_extract.cpp ;
+run project.cpp ;

test/project.cpp

@@ -0,0 +1,69 @@
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/lambda2.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <utility>
+
+struct X
+{
+    int m1;
+    int m2;
+
+    int f1() const
+    {
+        return m1;
+    }
+
+    int& f2()
+    {
+        return m2;
+    }
+};
+
+int main()
+{
+    using namespace boost::lambda2;
+
+    {
+        X const x{ 1, 2 };
+
+        BOOST_TEST_EQ( (_1->*&X::m1)( x ), 1 );
+        BOOST_TEST_EQ( (_1->*&X::m2)( x ), 2 );
+        BOOST_TEST_EQ( (_1->*&X::f1)( x ), 1 );
+    }
+
+    {
+        X x{ 0, 0 };
+
+        BOOST_TEST_EQ( (_1->*&X::m1)( x ), 0 );
+        BOOST_TEST_EQ( (_1->*&X::m2)( x ), 0 );
+        BOOST_TEST_EQ( (_1->*&X::f1)( x ), 0 );
+        BOOST_TEST_EQ( (_1->*&X::f2)( x ), 0 );
+
+#if defined(_LIBCPP_VERSION)
+
+        // https://bugs.llvm.org/show_bug.cgi?id=51753
+        using std::placeholders::_1;
+
+#endif
+
+        BOOST_TEST_EQ( (_1->*&X::m1 += 1)( x ), 1 );
+        BOOST_TEST_EQ( (_1->*&X::m2 += 2)( x ), 2 );
+
+        BOOST_TEST_EQ( (_1->*&X::f1)( x ), 1 );
+        BOOST_TEST_EQ( (_1->*&X::f2)( x ), 2 );
+
+        BOOST_TEST_EQ( (_1->*&X::f2 += 3)( x ), 5 );
+    }
+
+    {
+        std::pair<int, int> const x( 1, 2 );
+
+        BOOST_TEST_EQ( (_1->*&std::pair<int, int>::first)( x ), 1 );
+        BOOST_TEST_EQ( (_1->*&std::pair<int, int>::second)( x ), 2 );
+    }
+
+    return boost::report_errors();
+}