On Wed, 2008-04-09 at 15:40 +0200, Facchinetti Giorgio wrote:
> I am trying to use the LazyObject pattern, but I don't understand the
> reason behind the constness of calculate method.
Ciao Giorgio,
apologies for the delay. I agree that LazyObject::calculate doesn't
look much const. Unfortunately, it's going to be called inside methods
such as Instrument::NPV or YieldTermStructure::discount. These methods
must be const (conceptually, an instrument shouldn't change if you ask
for its value, so one should be able to call NPV on a const Instrument)
so they force LazyObject::calculate to be const as well. In turn, this
causes any cached data members to be mutable. It's not pretty, but it's
a common problem when caching calculations...
Luigi
--
Innovation is hard to schedule.
-- Dan Fylstra
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