examples do not build

[mgaunard]

../example/foldable.cpp:30:48: error: no member named 'str' in 'std::basic_ostream<char>'
            return (std::ostringstream{} << x).str();

This is with clang 3.6.0 885f51439b619bfc42e47c70bd3404ceedcf259f on Linux.

[mgaunard]

static_cast<std::ostringstream&>(std::ostringstream{} << x).str(); works well

[ldionne]

Here's what I think happens: std::ostringstream{} << x returns a std::basic_ostream<char> when it is used with a std::string, because the operator<< is defined as:

template<class _CharT, class _Traits, class _Allocator>
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
           const basic_string<_CharT, _Traits, _Allocator>& __str);

Then, we try to .str() that basic_ostream, which results in the provided error. I had never thought about the fact that operator<< would return a basic_ostream; I find that badly designed and counterintuitive. Still, I'll fix the examples.

Thanks for reporting.