Re: [Boost-users] [thread] Ambiguity in variadic wait_for_all

Le 03/02/2017 à 02:38, Gavin Lambert a écrit :

A colleague recently ran into an interesting issue when upgrading some working code from Boost 1.55 to 1.60/1.63 (and from C++03 to C++11).

The exact details are unimportant, but it was trying to get the address of boost::wait_for_all(Iterator, Iterator), for use in a Boost.Bind call.

In 1.55, this worked fine, although of course it had to supply template parameters that proved the parameters were not futures (thus causing enable_if to fail, disabling the two-future-args overload of the function.

In 1.60/1.63, the variadic method is encountered instead, which lacks any enable_if condition and thus the ambiguity between the two remains and the compiler errors out. (When calling it directly, the variadic one manages to get disabled as long as the iterator type lacks a wait() method, but this doesn't apply when just getting the method address, as it's not part of the signature.)

Should the variadic form also have enable_if? Or is this considered user error for trying to use Bind in a variadic-compatible compiler instead of using a lambda? Hi,

I will suggest you to replace the call to bind by lambdas whenever you can. You have made two changes IIUC, boost version and compiler version, so I don't know if this is a regression in boost 1.53 or a behavior that different between c++02 and C++11. I suspect that it is the change to C++11. Curiously I added enable if only for the function with two arguments, but not for the others. template typename boost::enable_if::type wait_for_all(F1& f1,F2& f2) When I added the C++11 version I surely forget to add the enable_if. Please, could you try to add the enable_if to the variadic template and tell me if this would fix your issue? template *typename boost::enable_if::type* wait_for_all(F1& f1, Fs&... fs) Best, Vicente