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: 2017-03-26 21:38:31

>> Indeed subsection 19.5.1.3 explicitly says that the comparison operator
>> returns (this == &rhs). That puts standard library implementators in a
>> bind.
> 
> It does. You should consider submitting a defect to LWG with the
> excellent description to wrote in your earlier reply.

Sorry, probably I wasn't clear: I *have* raised this with the committee
already, albeit informally. They are well aware of the problems
introduced by the use of shared objects on ELF in practice.

The problem is that C++ says nothing about shared object binaries.
Implicit throughout the standard is the assumption that monolithic
binaries are the sole thing ever produced by a linker, period, and in
that use case the standard mandated behaviour works perfectly. If you do
anything with C++ that is not generating a monolithic executable, you
are officially in UB land where monsters such as the problem described
lurk. You are *on your own*, and this is despite most C++ programmers
are in this UB land on a daily basis.

It is unfortunate that the Modules TS intentionally says absolutely
nothing about shared binaries. It could have been an opportunity to fix
these issues. But objections to that part of earlier proposals was
objected to very early, and they got dropped swiftly.

Niall

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