Re: Potential project: Resolving boost::chrono conflicts with std::chrono

From: Bjorn Reese (breese_at_[hidden])
Date: 2019-08-09 10:49:37

On 8/9/19 3:01 AM, Howard Hinnant via Boost wrote:

> The pitch:  boost::chrono, and other boost::libs needs to defer to std::chrono for C++11 and later.  This would make 

This should be done with great care.

Boost.Asio does exactly this for its timer classes -- use boost::chrono
if compiled pre-C++11 and otherwise use std::chrono.

As implemented, this is a pain from the users perspective, because the
user has to pass a type-strong expiration parameter which can be either,
say, std::chrono::seconds or boost::chrono::seconds. This means, that
your code that works perfectly suddenly yields compilation errors when
your users change the compiler flags.

   boost::asio::steady_timer timer;
   timer.expires_from_now(boost::chrono::seconds(5)); // Fails post C++03

The Boost.Asio way is to import all chrono symbols into its own
namespace:

   boost::asio::steady_timer timer;
   timer.expires_from_now(boost::asio::chrono::seconds(5)); // Okay

Another solution is to use the timer template classes, e.g.
basic_waitable_timer instead of steady_timer, so the user can work
around the problem by selecting whether to use std::chrono or
boost::chrono:

   boost::asio::basic_waitable_timer<boost::chrono::steady_clock> timer;
   timer.expires_from_now(boost::chrono::seconds(5)); // Okay

PS: I am not arguing for or against the project, nor am I recommending
any particular solution. I am just sharing some experience.