No warning on unused variable

[Andrew Haley]

Dave Williss writes:
 > 
 > >  > 
 > >  > Why did this not warn me about the unused stringstream?
 > > [snip]
 > > > it is concievable that declaring this object
 > >  > might be sufficient for some action to be taken by the code, thus
 > >  > rendering it incorrect for -Wall to report it.
 > >
 > > You got it in one.  For example, you might see
 > >
 > >   {
 > >     lock myLock;
 > >     ...  
 > >   }
 > >
 > > where the lock constructor locks memory and the destructor releases
 > > it.  
 > >   
 > It might be nice if g++ could add an __attribute__ setting so you could 
 > tag a class with something like ctor_has_no_useful_side_effects.  
 > Classes with this attribute could then be allowed to raise the "declared 
 > but not used" warning.  It would be most useful on things like 
 > std::string, which you also wouldn't want just laying around.

It's an interesting idea, for sure.  I can't immediately think of any
big downside, but I'm not sure if such a patch would be accepted.

Andrew.