Terje Slettebø <tslettebo@broadpark.no> writes:
enable_if doesn't always improve error messages. Sometimes you get a long list of candidate functions when what you really wanted was a message from inside just one of the overloads that indicates how concept conformance was violated.
How can you get a list of candidate functions, if enable_if excludes them from the overload set? Could you give a code example?
#include <boost/utility/enable_if.hpp> #include <boost/type_traits/is_same.hpp> template <class T> typename boost::enable_if<boost::is_same<T,int>,int>::type f(T); template <class T> typename boost::enable_if<boost::is_same<T,long*>,int>::type f(T); int main() { f("foo"); } CWPro9: ### mwcc Compiler: # File: foo.cpp # ---------------- # 14: f("foo"); # Error: ^ # function call 'f({lval} const char[4])' does not match # 'f<...>(__T0)' # 'f<...>(__T0)' VC7.1: foo.cpp foo.cpp(14) : error C2893: Failed to specialize function template 'boost::enable_if< boost::is_same<T, long *>, int >::type f(T)' With the following template arguments: 'const char *' foo.cpp(14) : error C2893: Failed to specialize function template 'boost::enable_if< boost::is_same<T, int>, int >::type f(T)' With the following template arguments: 'const char *' And even when there's no list as with GCC, "no match" is usually less-useful than "here's what's wrong with the argument." -- Dave Abrahams Boost Consulting http://www.boost-consulting.com