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Subject: Re: [boost] [contract] auto_..._error regression tests fail on C++1z
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2017-10-04 16:48:59

On Tue, Oct 3, 2017 at 11:45 PM, Andrzej Krzemienski via Boost
<boost_at_[hidden]> wrote:
> 2017-09-29 4:29 GMT+02:00 Lorenzo Caminiti via Boost <boost_at_[hidden]>
>> Is there any way to make that `auto xx = f()` in main fail at compile
>> time in C++1z?
> But why do you want this program to fail to compile?

The library requires to explicitly use `boost::contract::check c =
boost::contract::function()`. Using `auto c =
boost::contract::function()` or `boost::contract::function()` (without
assigning it to anything) will generate a run-time error. This is well
documented. On non C++1z compilers, the library will also give a
compile-time error if `auto c = boost::contract::function()` is used
by mistake (but this no longer fails compilation on C++1z so you are
left with just the run-time error in that case on C++1z).

In summary, this is just to catch a misuse of the API at compile-time
instead of run-time... this is well documented so it shouldn't be a
real issue in practice.

P.S. I'm surprised that I can no longer write a type in C++1z that
will fail compilation when used via its copy operations... I wonder if
that is an unintended consequence of the zero-copy optimization
guarantee that C++1z has. Sure no copies should be made at run-time,
but I should still get a compile-time error if I try to use a copy
operation on a type that does allow copy, even when these copies are
guaranteed to be optimized away in C++11z.


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