Re: [boost] [operators] The Dangling Reference Polarization

Subject: Re: [boost] [operators] The Dangling Reference Polarization
From: Andrew Ho (helloworld922_at_[hidden])
Date: 2013-04-25 17:32:30

> It seems that this is consistent behavior across at least GCC, Clang and 
VC++. If a compiler shows a different behavior, its likely a compiler-bug.

VS2012 behaves differently. Not only is T &a = b + c + d not a compile error, 
but in all cases I've tested the temporary's life is actually extended! I'll 
raise questions to MS to get their input to see if they intended this, or if 
it's a bug (never know which it is with MS). My tests with GCC does mirror 
your observations.

> d) I fail to see any valid use-case for binding the result of the expression 
to a reference. Can someone
> please provide a convincing example of why (P1) or (P2) are needed/useful? 
Keep in mind that in the context
> of operator+ (or any other operator in question), we already require that 
the type T is copy-/moveable and
> that copy-elision most likely takes place if you use "T r = …" instead of 
"const T& r = …".

Found one which fails with gcc 4.7.2 (again, VS2012's trickery extends object 
lifetimes so it "works"):

for(char c : str1 + str2 + str3)
{
    // ...
}

The temporary returned is destructed prematurely.