id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
11705	Phoenix function defining operator() with non-const reference parameter fails to compile with C++ 11.	David Williams <bateyware@…>	Thomas Heller	"A phoenix function object defining operator() with a non-const reference parameter does not compile when using clang version 3.5 in C++ 11 mode.

The compiler used is: Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)

The Boost version used is 1.59.

A test program to illustrate the problem along with the compiler build log are provided with this bug report.

An example of such a function object that reproduces the problem is the following:

struct add_int_impl
{
typedef int result_type;

add_int_impl(int v)
{
	_value=v;
}

int operator()(bool& flag) const
{
	std::cout << ""int operator()(bool& flag) called"" << std::endl;
	if (_value == 4)
		flag=true;
	return _value;
}

 int _value;
};

The function can be tested with the following code snippet:

// *** Begin code snippet ***

// Initialise the function with the value 4.

boost::phoenix::function<add_int_impl> add_int(4);	

bool flag=false;

BOOST_TEST(add_int(arg1)(flag) == (4));

// *** End code snippet ***

This call will only compile under Apple's version of clang 3.5 in C++ 11 mode when one or both of the
following conditions are met;

1) The int operator()(int a) const is also defined

2) One of the following flags is defined:

BOOST_RESULT_OF_TR1
BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK

The program also compiles if the function signature is changed to use a const 
reference parameter, i.e. int operator()(const bool& flag) const.
However this then means that the parameter value cannot be
modified within the body of the function as required.

The problem does not occur if the program is compiled using C++ 98 compatibility mode.

I suspect that the problem relates to the use of boost::result_of, which uses the decltype() function
to deduce function return types when compiling with C++ 11 support.

    
"	Bugs	new	To Be Determined	phoenix	Boost 1.59.0	Problem		phoenix function, C++ 11, result_of