Special-case streams in operator<< and operator>>

include/boost/lambda2/lambda2.hpp

@@ -10,6 +10,7 @@
 #include <utility>
 #include <tuple>
 #include <cstddef>
+#include <iosfwd>
 
 // Same format as BOOST_VERSION:
 //   major * 100000 + minor * 100 + patch
@@ -201,9 +202,6 @@ BOOST_LAMBDA2_UNARY_LAMBDA(~, std::bit_not<>)
 
 // additional
 
-BOOST_LAMBDA2_BINARY_LAMBDA(<<, lambda2_detail::left_shift)
-BOOST_LAMBDA2_BINARY_LAMBDA(>>, lambda2_detail::right_shift)
-
 BOOST_LAMBDA2_UNARY_LAMBDA(+, lambda2_detail::unary_plus)
 BOOST_LAMBDA2_UNARY_LAMBDA(*, lambda2_detail::dereference)
 
@@ -226,6 +224,38 @@ BOOST_LAMBDA2_BINARY_LAMBDA(^=, lambda2_detail::bit_xor_equal)
 BOOST_LAMBDA2_BINARY_LAMBDA(<<=, lambda2_detail::left_shift_equal)
 BOOST_LAMBDA2_BINARY_LAMBDA(>>=, lambda2_detail::right_shift_equal)
 
+// operator<<
+
+template<class A, class = std::enable_if_t<!std::is_convertible<A&, std::ios_base&>::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) ); \
+}
+
+template<class A, class = std::enable_if_t<std::is_convertible<A&, std::ios_base&>::value>,
+    class B, class = lambda2_detail::enable_unary_lambda<B>>
+auto operator<<( A& a, B&& b )
+{
+    return std::bind( lambda2_detail::left_shift(), std::ref(a), std::forward<B>(b) );
+}
+
+// operator>>
+
+template<class A, class = std::enable_if_t<!std::is_convertible<A&, std::ios_base&>::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) ); \
+}
+
+template<class A, class = std::enable_if_t<std::is_convertible<A&, std::ios_base&>::value>,
+    class B, class = lambda2_detail::enable_unary_lambda<B>>
+auto operator>>( A& a, B&& b )
+{
+    return std::bind( lambda2_detail::right_shift(), std::ref(a), std::forward<B>(b) );
+}
+
 } // namespace lambda2
 } // namespace boost
 

test/Jamfile

@@ -24,3 +24,5 @@ run placeholders.cpp ;
 run increment.cpp ;
 run subscript.cpp ;
 run compound.cpp ;
+run stream_insert.cpp ;
+run stream_extract.cpp ;

test/stream_extract.cpp

@@ -0,0 +1,28 @@
+// 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 <sstream>
+#include <string>
+
+template<class T> T from_string( std::string const& s )
+{
+    using namespace boost::lambda2;
+
+    std::istringstream is( s );
+
+    T t{};
+
+    ( is >> _1 )( t );
+
+    return t;
+}
+
+int main()
+{
+    BOOST_TEST_EQ( from_string<int>( "123" ), 123 );
+
+    return boost::report_errors();
+}

test/stream_insert.cpp

@@ -0,0 +1,26 @@
+// 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 <sstream>
+#include <string>
+
+template<class T> std::string to_string( T const& t )
+{
+    using namespace boost::lambda2;
+
+    std::ostringstream os;
+
+    ( os << _1 )( t );
+
+    return os.str();
+}
+
+int main()
+{
+    BOOST_TEST_EQ( to_string( 123 ), "123" );
+
+    return boost::report_errors();
+}