[std-interval] default constructor

[Gabriel Dos Reis]

Guillaume Melquiond <guillaume.melquiond at ens-lyon.fr> writes:

| Le mercredi 05 avril 2006 à 05:13 -0600, Alan Eliasen a écrit :
| 
| >    I think that there should *never* be a zero-arg default constructor
| > for intervals.  All constructors should have at least one argument to
| > force the programmer to declare their intent.
| 
| This is too strong a requirement. Forbidding arrays of intervals is a
| sure way of alienating any C++ user.

Indeed, that is an excellent observation.  It is good to take into
account experience of interval libraries in other languages; we must
however not forget ways C++ is natively used.

-- Gaby