A Special Note for Boost 1.52.0 and Higher
A Special Note for Boost 1.52.0 and Higher
November 6th, 2012 09:27 GMT
Starting with Boost 1.52.0, the boost::result_of
component defaults to an implementation that uses the C++11 decltype
keyword to deduce the return type of callables on compilers with strong decltype support. As boost::result_of
is a key piece of library infrastructure, we at Boost have found this change
to be moderately disruptive. You should be aware of the issue when making the
decision to upgrade from an older version of Boost.
Why the Change Was Made
boost::result_of has been changed to use decltype to make it more consistent with std::result_of
(when sufficient compiler support is available). Also, the use of decltype should help to improve compile times
and increase the accuracy of the type computation.
Who is Affected
If you use a compiler with sufficiently bug-free decltype
support (including N3276),
then you will get the new behavior. At the time of writing (Nov 4, 2012), the
only compiler in that category is Clang 3.1, but as other compilers improve,
this will change.
What Problems Can the Change Cause?
The use of decltype in result_of can result in a different type
being computed than with the now-obsolete TR1 result_of
protocol. This will often be the case for incorrectly written TR1-style function
objects that misreport their result types. This is unfortunately too common.
But it can even happen for some correctly written function objects.
Where Can I Learn More?
Please see the documentation for boost::result_of
to understand the differences between TR1 result_of
and decltype result_of,
and to find out how you can write your code to accommodate both.
