Add boost::ignore_unused()

doc/core.qbk

@@ -37,6 +37,10 @@ Currently, the Core library contains:
    [[@../../enable_if.html enable_if]]
    [`boost::enable_if`]
  ]
+ [
+   [[link core.ignore_unused ignore_unused]]
+   [`boost::ignore_unused`]
+ ]
  [
    [[link core.lightweight_test lightweight_test]]
    [`BOOST_TEST, BOOST_ERROR, BOOST_TEST_EQ, BOOST_TEST_NE,
@@ -74,6 +78,7 @@ Currently, the Core library contains:
 
 [include:core addressof.qbk]
 [include:core explicit_operator_bool.qbk]
+[include:core ignore_unused.qbk]
 [include:core lightweight_test.qbk]
 [include:core no_exceptions_support.qbk]
 [include:core noncopyable.qbk]

doc/ignore_unused.qbk

@@ -0,0 +1,29 @@
+[section:ignore_unused Header <boost/core/ignore_unused.hpp>]
+
+The header `<boost/core/ignore_unused.hpp>` defines the function template
+`boost::ignore_unused()`. It may be used to suppress the "unused variable" or
+"unused local typedefs" compiler warnings when the variable or typedef
+can't be removed or commented out, e.g. when some blocks of the code are
+conditionally activated. C++11 variadic templates are used if they're supported,
+otherwise they're emulated with overloads.
+
+`boost::ignore_unused()` was contributed by Adam Wulkiewicz.
+
+Usage
+
+    boost::ignore_unused(v1, v2, v3);
+    boost::ignore_unused<T1, T2, T3>();
+
+Example
+
+    int fun( int foo, int bar )
+    {
+       boost::ignore_unused(bar);
+    #ifdef ENABLE_DEBUG_OUTPUT
+       if ( foo < bar )
+          std::cerr << "warning! foo < bar";
+    #endif
+       return foo + 2;
+    }
+
+[endsect]

include/boost/core/ignore_unused.hpp

@@ -0,0 +1,70 @@
+// Copyright (c) 2014 Adam Wulkiewicz, Lodz, Poland.
+//
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_CORE_IGNORE_UNUSED_HPP
+#define BOOST_CORE_IGNORE_UNUSED_HPP
+
+#include <boost/config.hpp>
+
+namespace boost {
+
+#ifndef BOOST_NO_CXX11_VARIADIC_TEMPLATES
+
+template <typename... Ts>
+inline void ignore_unused(Ts const& ...)
+{}
+
+template <typename... Ts>
+inline void ignore_unused()
+{}
+
+#else
+
+template <typename T1>
+inline void ignore_unused(T1 const&)
+{}
+
+template <typename T1, typename T2>
+inline void ignore_unused(T1 const&, T2 const&)
+{}
+
+template <typename T1, typename T2, typename T3>
+inline void ignore_unused(T1 const&, T2 const&, T3 const&)
+{}
+
+template <typename T1, typename T2, typename T3, typename T4>
+inline void ignore_unused(T1 const&, T2 const&, T3 const&, T4 const&)
+{}
+
+template <typename T1, typename T2, typename T3, typename T4, typename T5>
+inline void ignore_unused(T1 const&, T2 const&, T3 const&, T4 const&, T5 const&)
+{}
+
+template <typename T1>
+inline void ignore_unused()
+{}
+
+template <typename T1, typename T2>
+inline void ignore_unused()
+{}
+
+template <typename T1, typename T2, typename T3>
+inline void ignore_unused()
+{}
+
+template <typename T1, typename T2, typename T3, typename T4>
+inline void ignore_unused()
+{}
+
+template <typename T1, typename T2, typename T3, typename T4, typename T5>
+inline void ignore_unused()
+{}
+
+#endif
+
+} // namespace boost
+
+#endif // BOOST_CORE_IGNORE_UNUSED_HPP

test/Jamfile.v2

@@ -36,4 +36,8 @@ test-suite "core"
         [ compile-fail explicit_operator_bool_compile_fail_conv_pvoid.cpp ]
         [ compile-fail explicit_operator_bool_compile_fail_delete.cpp ]
         [ compile-fail explicit_operator_bool_compile_fail_shift.cpp ]
+
+	[ compile ignore_unused_test.cpp : <toolset>gcc:<cxxflags>"-Wunused-variable -Wunused-local-typedefs -Werror"
+                                           <toolset>clang:<cxxflags>"-Wunused-variable -Werror"
+                                           <toolset>msvc:<cxxflags>"/we4100 /we4101" ]
     ;

test/ignore_unused_test.cpp

@@ -0,0 +1,65 @@
+// Copyright (c) 2014 Adam Wulkiewicz, Lodz, Poland.
+//
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//#include <boost/utility/ignore_unused.hpp>
+#include <boost/utility.hpp>
+
+int main()
+{
+    {
+        int a;
+        boost::ignore_unused(a);
+    }
+    {
+        int a, b;
+        boost::ignore_unused(a, b);
+    }
+    {
+        int a, b, c;
+        boost::ignore_unused(a, b, c);
+    }
+    {
+        int a, b, c, d;
+        boost::ignore_unused(a, b, c, d);
+    }
+    {
+        int a, b, c, d, e;
+        boost::ignore_unused(a, b, c, d, e);
+    }
+
+    {
+        typedef int a;
+        boost::ignore_unused<a>();
+    }
+    {
+        typedef int a;
+        typedef int b;
+        boost::ignore_unused<a, b>();
+    }
+    {
+        typedef int a;
+        typedef int b;
+        typedef int c;
+        boost::ignore_unused<a, b, c>();
+    }
+    {
+        typedef int a;
+        typedef int b;
+        typedef int c;
+        typedef int d;
+        boost::ignore_unused<a, b, c, d>();
+    }
+    {
+        typedef int a;
+        typedef int b;
+        typedef int c;
+        typedef int d;
+        typedef int e;
+        boost::ignore_unused<a, b, c, d, e>();
+    }
+
+    return 0;
+}