Re: std::pair istream >> operator
The solution I'd always seen (in pre-standard complex) was to
apply (width()-3)/2 to each of the components of the complex.
The draft standard says about stream::operator<<
Effects: inserts the complex number x onto the stream o as if it were
implemented as follows:
template<class T, class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& o, const complex<T>& x)
{
basic_ostringstream<charT, traits> s;
s.flags(o.flags());
s.imbue(o.getloc());
s.precision(o.precision());
s << '(' << x.real() << "," << x.imag() << ')';
return o << s.str();
}
If I could put in a recommendation it would be:
- Add a separator field to the ios_base structure (default =
traits::eof() -> ctype.isspace for input and space for output)
- Add manipulators: separator, setseparator, showseparator,
noshowseparator (default)
- Width, fill etc applies to each item (but not the separator)
- separator is also used to end stream input for string.
None of which addresses the basic problem of outputting
std::pair (or boost::tuple): the fact that the type may have
different semantic signification at different places in the
program.
Isn't that something that applies to all types?
Built in types like double got modifers on format, precision etc. If
you need some non-standard formatting you implement your own but it
still nice to have a default.
Although there may be some special cases, my own feeling is that
any use of std::pair (and probably most uses of boost::tuple)
are simply poor programming.
I agree but admit I'm using them a lot. Specially in containers.
To make your own "named_tuple" you need to implement the operators as
well. I have some macros to do it but it quickly get inconvenient.
If I temporary need a set or map with 2 values inside a funtion I just
do a single line
typedef std::map<int, std::pair<std::string, int> > mymap;
To do it with a macro you first need to create the type outside the
function (template types need external linkage) which could be in .h
file somewhere.
NAMED_TUPLE(mytuple, std::string, name, int, value);
..
typedef std::map<int, mytuple> mymap;
It would be nice with a feature like the anonymous types in C# 3.
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