Re: [boost] [test] BOOST_TEST macro and std::max

2016-01-11 13:46 GMT+01:00 Raffi Enficiaud :

Le 11/01/16 10:51, Andrzej Krzemienski a écrit :

2016-01-11 4:11 GMT+01:00 Gennadiy Rozental :

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Benedek Thaler writes:

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I believe at this point we understand WHAT is going on.

auto const& E = ::boost::test_tools::assertion::seed()->*3u

...

== ((std::max)(0u, 3u));

max returns unsigned int&&, which for some unclear reason is bound to unsigned int const& in expression template E. This obviously becomes dangling reference as soon as we leave this line.

This is an expected behavior in C++: an xvalue (rvalue reference returned from a function) can be bound to a const lvalue reference. See example: http://melpon.org/wandbox/permlink/yon7EWpj2B5KQNcT

This is a nice web site :) (I should update myself)

The example here is more what is happening: http://melpon.org/wandbox/permlink/R2obgUazntZM9LVT

the "printit" function with an universal ref. The return of std::max with two identical types is a const lvalue ref according to the standard.

That ref lifetime is expanded until what point?

The "binary_expr" that is returned with boost.test holds that ref. The code is

template<typename T> binary_expr > operator==( T&& rhs ) { // ...

Is this ref valid at the return of operator== ?

In the case of

auto const& E = ::boost::test_tools::assertion::seed()->*3u == ((std::max)(0u, 3u)) ;

that ref would exists until " ; ", but if "E" contains an object having this reference, it is dandling after the " ; ".

Yes, a member reference inside E is dangling after " ; ". Member references do not prolong the life-time of temporary objects.