on Thu Oct 11 2012, Andrew Sutton <asutton.list-AT-gmail.com> wrote:
Look for example at http://www.sgi.com/tech/stl/find_if.html. I can easily satisfy all the stated requirements and produce an example that won't compile. I can also easily fail to satisfy the stated requirements and produce an example that *will* compile. That's because there's a great deal of potential mischief hiding in expressions such as
f(*p)
Can you produce those examples? You've made me curious.
Doesn't compile, but "should" --8<---------------cut here---------------start------------->8--- #include <algorithm> #include <vector> struct Predicate { typedef char argument_type; bool operator()(char) const; bool operator()(long) const; }; std::vector<int> v(10); std::vector<int>::iterator p = std::find_if(v.begin(), v.end(), Predicate()); --8<---------------cut here---------------end--------------->8--- If you take the standard definition of "input iterator" instead of the SGI one, the examples are even more compelling, because the result type of "*p" merely has to be "convertible to T", so it's easy to arrange a Predicate with no overloads that fails to accept the argument because too many implicit conversions are required. For the "shouldn't compile, but does" example I was presuming the standard definition of "input iterator;" just make an input iterator that returns a type X convertible to the value type, and make the predicate's operator() accept X but not the value type. -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost