Re: [Boost-users] Compare boost::system::error_category

Subject: Re: [Boost-users] Compare boost::system::error_category
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-03-25 23:24:32

On 25/03/2017 23:05, Christopher Pisz via Boost-users wrote:
> What would be so wrong with category being an actual number to
> compare against?
> 
> I don't know anyone whom creates classes and operator == using the 
> address of that class. You guys talk about the standard and what
> not, and admittedly I've never looked inside how they implement
> things, but I've never had such problems using the STL either.

C++ 14 standard subsection 19.5.1.1:

"error_category objects are passed by reference, and two such objects
are equal if they have the same address. This means that applications
using custom error_category types should create a single object of each
such type."

Indeed subsection 19.5.1.3 explicitly says that the comparison operator
returns (this == &rhs). That puts standard library implementators in a bind.

Niall

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