Idea for more delegations in <algorithm>

[Gabriel Dos Reis]

Paolo Carlini <pcarlini@suse.de> writes:

| Hi everyone, hi Chris,
| 
| today I got an idea, or better I *read* an idea: do you know N1758?
| Basically, Siek et al., explain at pag. 37 how to to do dispatching
| without tag types. Nothing very exoteric, actually, if you know
| enable_if, but this strikes me as potentially solving at the root the
| optimization problems with empty classes! Because we do *not* have
| additional parameters in the function calls!
| 
| For instance, they implement "do the right thing" for vector as:
| 
|     template<typename InputIterator>
|        vector<InputIterator first, InputIterator last,
|                    typename
| enable_if<(!is_integral<InputIterator>::value), void*>::type = 0);
| 
| Or, for some reason, we have troubles with this too? :(

While I've committed my own share of enable-if sins, I've always been
very reluctant to spread it anywhere unless there really is no
acceptable alternative within the language.  For vector<>, we already have
the dispatching stuff already in place, so I would not recommend that
approach. (Note too that insert()  require the same thing and it is an
ABI change).

-- Gaby