Update documentation

doc/lambda2.adoc

@@ -9,6 +9,7 @@ Peter Dimov
 :toc: left
 :toclevels: 4
 :idprefix:
+:listing-caption: Code Example
 :docinfo: private-footer
 
 :leveloffset: +1

doc/lambda2/changelog.adoc

@@ -12,3 +12,5 @@ https://www.boost.org/LICENSE_1_0.txt
 
 * Added special cases in `operator<<` and `operator>>` when
   the first argument is a stream, to allow `std::cout << _1`.
+* Added `operator\->*`.
+* Added `first`, `second`.

doc/lambda2/reference.adoc

@@ -21,14 +21,14 @@ namespace lambda2 {
 template<int I> struct lambda2_arg;
 
 inline constexpr lambda2_arg<1> _1{};
-inline constexpr lambda2_arg<1> _2{};
+inline constexpr lambda2_arg<2> _2{};
-inline constexpr lambda2_arg<1> _3{};
+inline constexpr lambda2_arg<3> _3{};
-inline constexpr lambda2_arg<1> _4{};
+inline constexpr lambda2_arg<4> _4{};
-inline constexpr lambda2_arg<1> _5{};
+inline constexpr lambda2_arg<5> _5{};
-inline constexpr lambda2_arg<1> _6{};
+inline constexpr lambda2_arg<6> _6{};
-inline constexpr lambda2_arg<1> _7{};
+inline constexpr lambda2_arg<7> _7{};
-inline constexpr lambda2_arg<1> _8{};
+inline constexpr lambda2_arg<8> _8{};
-inline constexpr lambda2_arg<1> _9{};
+inline constexpr lambda2_arg<9> _9{};
 
 // arithmetic operators
 
@@ -90,6 +90,11 @@ template<class A, class B> auto operator>>=( A && a, B && b );
 
 template<class A, class B> auto operator->*( A && a, B && b );
 
+// projections
+
+inline constexpr /unspecified/ first{};
+inline constexpr /unspecified/ second{};
+
 } // namespace lambda2
 } // namespace boost
 ```
@@ -405,3 +410,26 @@ 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`.
+
+### Projections
+
+```
+inline constexpr /unspecified/ first{};
+```
+
+A function object such that `first(x)` returns `std::get<0>(x)`.
+
+```
+inline constexpr /unspecified/ second{};
+```
+
+A function object such that `second(x)` returns `std::get<1>(x)`.
+
+.Using first and second to print out a map
+```
+void print( std::map<int, std::string> const & m )
+{
+    using namespace boost::lambda2;
+    std::for_each( m.begin(), m.end(), std::cout << _1->*first << ": " << _1->*second << '\n' );
+}
+```

include/boost/lambda2/lambda2.hpp

@@ -32,6 +32,14 @@ struct subscript
     }
 };
 
+template<int I> struct get
+{
+    template<class T> decltype(auto) operator()( T&& t ) const
+    {
+        return std::get<I>( std::forward<T>(t) );
+    }
+};
+
 } // namespace lambda2_detail
 
 // placeholders
@@ -65,6 +73,11 @@ BOOST_LAMBDA2_INLINE_VAR constexpr lambda2_arg<7> _7{};
 BOOST_LAMBDA2_INLINE_VAR constexpr lambda2_arg<8> _8{};
 BOOST_LAMBDA2_INLINE_VAR constexpr lambda2_arg<9> _9{};
 
+// first, second
+
+BOOST_LAMBDA2_INLINE_VAR constexpr lambda2_detail::get<0> first{};
+BOOST_LAMBDA2_INLINE_VAR constexpr lambda2_detail::get<1> second{};
+
 #undef BOOST_LAMBDA2_INLINE_VAR
 
 } // namespace lambda2

test/project.cpp

@@ -63,6 +63,16 @@ int main()
 
         BOOST_TEST_EQ( (_1->*&std::pair<int, int>::first)( x ), 1 );
         BOOST_TEST_EQ( (_1->*&std::pair<int, int>::second)( x ), 2 );
+
+#if defined(_LIBCPP_VERSION)
+
+        // https://bugs.llvm.org/show_bug.cgi?id=51753
+        using std::placeholders::_1;
+
+#endif
+
+        BOOST_TEST_EQ( (_1->*first)( x ), 1 );
+        BOOST_TEST_EQ( (_1->*second)( x ), 2 );
     }
 
     return boost::report_errors();