[boost] std_min/std_max reference return value is problematic with boost::interval

From: Michael Stevens (Michael.Stevens_at_[hidden])
Date: 2004-03-08 12:53:00

Eric,

The recent changes to the new std_min/std_max caused some unexpected problems 
in uBLAS. I have narrowed them down to support for boost::numeric::interval 
in uBLAS. This is picked up by ublas/libs/test7. This test is however not at 
present part of the regression run.

The new std_max (or std_min) is implemented by returning a constant reference 
to the return value of std::max. This should be OK as std::max similarly 
returns a const reference to one of its const reference parameters.  For gcc 
this causes some problems when the type is a boost::numeric::interval. The 
test case is very simple.

#include <boost/numeric/interval.hpp>
#include <boost/minmax.hpp>

int main()
{
        boost::numeric::interval<float> a,b,c;
        c = boost::std_max(a, a);
}

gcc (2.95.3 and 3.3.1) is only warning "returning reference to temporary". I 
am surprised this doesn't show up in more cases. Why gcc thinks it needs a 
temporary here is beyond me

Michael
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Michael Stevens Systems Engineering
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