[Bug c++/54047] unused variable warning not for std::string

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54047

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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           Keywords|                            |diagnostic

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-07-20 12:09:01 UTC ---
It's the case for all objects with a non-trivial constructor, not only
std::string.

Constructors might have side-effects, so you might not need to "use" the
variable, all you want is to construct it.

e.g. you don't want an unused variable warning for 'l' here:

  void f(std::mutex& m, int& i) {
    std::lock_guard<std::mutex> l(m);
    i = 1;
  }

I think this behaviour is intentional and correct.