I am having a problem with Boost.Bind (1.33.1). Consider the following simplified code: struct Bob { void func() { } }; void bob_test() { typedef std::map BobMap; BobMap bob_map; std::for_each(bob_map.begin(), bob_map.end(), bind(&Bob::func, bind(&BobMap::value_type::second, _1))); } This fails to compile under DevStudio 8. The problem is the outer bound functor expects (Bob* const) but is passed (Bob const*). This seems a straight forward use -- call the "func" method on every Bob instance in the map. I can get this to compile if I change the inner bind to "bind(...)". Shouldn't the default return type of the binding of (R T::*) be (R&)? I looked through the bind and mem_fn documentation and didn't see any mention of that. The .* operator applied to a non-const T and a (R T::*) returns (R&), so it is implied that mem_fn of a data member does as well. Also, why does the error message refer to pointers and not references? Is that an artifact of compiler argument matching failure? Exact message: 1>inc\boost/bind/mem_fn_template.hpp(31) : error C2440: 'argument' : cannot convert from 'const Bob *' to 'Bob *const ' 1> inc\boost/bind/mem_fn_template.hpp(56) : see reference to function template instantiation 'R boost::_mfi::mf0::call<const U>(U &,const T *) const' being compiled 1> with 1> [ 1> R=void, 1> T=Bob, 1> U=Bob 1> ]

At 06:31 PM 1/16/2007, Peter Dimov wrote:

I assumed that writing bind won't be that big of a deal in the relatively rare cases where it's needed.

It sure beats not using bind(). I would recommend that the documentation be changed to reflect this, rather than claim compatibility with the .* operator as it does now. E.g. [...] where R is the return type of X::f (for member functions). For data members, the return value is by default (R const&) because the bind() generated functor must have this fixed upon creation, before it is known whether the argument will be const or not. If you need an lvalue, use the return type template argument of bind() to force the return type to be a non-const reference.