Hi François,
On Wed, 2007-09-05 at 16:12 +0200, DU VIGNAUD DE VILLEFORT FRANCOIS
GASAPRD PHI wrote:
> A quick question about the DerivedQuote class design: The operation
> performed by this class is a template parameter yet the actual
> operation is actually known only at run time.
No, it is usually known at compile-time. The current implementation of
value() calls operator() on the passed UnaryFunction instance, whose
type is usually known (we're taking a copy of it, so there's no
polymorphic behavior) and whose code can be inlined. The cases in which
this is not possible is just when UnaryFunction is a function pointer
(in the C style.)
> What about using a more informative template so that the operation
> can be known at compilation time and inlined ? (we would loose the
> possibility to change the operation at run time but who cares ?).
>
> To be as explicit as possible, the DerivedQuote value method would be
> written like this:
>
> template <class UnaryFunction>
>
> inline Real DerivedQuote<UnaryFunction>::value() const {
>
> QL_ENSURE(isValid(), "invalid DerivedQuote");
>
> return UnaryFunction::eval(element_->value());
>
> }
You mean, eval() should be a static method of the UnaryFunction class?
Unfortunately, this would mean that:
a) you can't use existing functions (which have no methods at all) or
function objects (which define operator() instead) unless you adapt
them;
b) you can't use function objects that hold non-static data
members---not even by adapting them.
Luigi
--
For every problem there is one solution which is simple, neat, and
wrong.
-- H. L. Mencken
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