Wpotentially-evaluated-expression raised on clang-3.6

[tomhenderson]

on Xcode 7 or clang-3.6, ns-3 bindings generated by pybindgen raise many warnings such as below for potentially evaluated expression in the argument:

src/topology-read/bindings/ns3module.cc:1482:16: error: expression with side effects will be evaluated despite being used as an operand to 'typeid' [-Werror,-Wpotentially-evaluated-expression]
if (typeid((*const_cast<ns3::Node *> (ns3::PeekPointer (retval)))).name() == typeid(PyNs3Node__PythonHelper).name())

To reproduce, check out ns-3.24 release (not ns-3.24.1) and compile with python bindings enabled on either clang-3.6 or Xcode 7.0 machine (may have to disable Werror).

We are suppressing this for now in the wscript, but I wonder if an upstream fix is possible to move the possibly side-effect-inducing expression out of the argument.

[gjcarneiro]

Hm, I wonder which "side effects" the compiler means. I am not aware of any side effects here... AFAIK, (*const_cast (ns3::PeekPointer (retval))) has no side effects, but I'd have to check more closely...

template <typename U>
U * PeekPointer (const Ptr<U> &p)
{
  return p.m_ptr;
}

[gjcarneiro]

I can't figure this one out. Tried adding __attribute__ ((pure, const)) to the PeekPointer definition, clang still complains. I am writing this off as a clang bug. Not fixing pybindgen.