Re: [boost] Reforming Boost.System and <system_error> round 2

Subject: Re: [boost] Reforming Boost.System and <system_error> round 2
From: Peter Dimov (lists_at_[hidden])
Date: 2018-01-16 17:09:51

Andrey Semashev wrote:

> Calling (virtual) `error_category::failure` early is a waste if the user 
> doesn't want to call that function himself. For instance, he may want to 
> test specific error codes instead.

It can still be worth it because it's more likely to occur in a context 
where the compiler can see what category is being used. When you have

    error_code ec( r, system_category() );

and system_category() is constexpr, the compiler knows with certainty what 
the call category().failed( r ) will do, so it will replace it with r != 0.