On Saturday, August 23, 2003, at 11:21 AM, Daniel Frey wrote:
Short-circuiting can only be done via compiler magic with the built-in operator&& and operator||, so there's no way it can be added to user-defined routines. Note that each step of the lexicographica) Short-circuiting b) Unnamed functions
macros and ?: can - as I showed - do short-circuiting, too. User-defined functions - as you said - can't.
comparison has a result, and that later steps are only evaluated if the previous step didn't give a result of equivalence (well, the comparison is skipped; each argument still has to be evaluated). You can also
Evaluation of arguments is IMO the problem.
manually check each intermediate result and code out other checks (with "if" statements), which would skip unnecessary evaluations of later components.
The point is, that Jan proposed to add something which has a hidden overhead and I'm not sure it's a good idea. Instead of nested if-else-cascades, the user could also write:
bool operator<( const person& lhs, const person& rhs )
{
return
lhs.lastname != rhs.lastname ? lhs.lastname < rhs.lastname :
lhs.firstname != rhs.firstname ? lhs.firstname < rhs.firstname :
lhs.age < rhs.age;
}This scheme is easy to remember, (IMHO) easy to read, doesn't have nested if's and it has short-circuiting. It's only cost which may be removed by Jan's proposal is that it removes the redundancy in typing. A per line-macro could do that without further problems, but I won't use it anyway. Sometimes I prefer to see the real code, hiding something needs a better rationale IMO. So we need some very convincing arguments for a new utility if we have to remove the short-circuiting.
Also, you might not want to define operator<. Sometimes, you just need it in one place, e.g. std::sort( v.begin(), v.end(), /*HERE*/ );
Maybe Boost.Lamda or Boost.MPL can be used?
Sure, but if the syntax becomes too complicated, users will stick with the if-else-way. Lambda and MPL might be too complicated for such a small helper. I think the proposed helper was meant to have an easy syntax, but maybe I'm reading Jan's proposal the wrong way.
I don't think you can (re#)define a keyword.
You can. But I admit that it's a stupid idea to do it, which is why I don't honestly propose to use true()/false()-macros :)
Regards, Daniel
-- Daniel Frey
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