[boost] Re: dynamic inheritance with FC++

From: Larry Evans (cppljevans_at_[hidden])
Date: 2004-02-28 10:05:00

On 02/28/2004 08:24 AM, Larry Evans wrote:
 > On 02/28/2004 08:08 AM, Larry Evans wrote:
 >
 >> On 02/27/2004 11:01 PM, Brian McNamara wrote:
 >
 > [snip]
 > One thing I forgot to emphasize is that this design pattern seeks
[snip]

Ok, maybe just one more thing: tree<B> has additional virtual
functions.  This, in essence, distinguishes this pattern from the
"pattern" implemented by boost graph properties AFAICT.  I really
haven't looked closely at graph properties, but I assume they don't
have virtual methods associated with the added properties.  What I
need is a virtual function associated with the new property.  For
example, the regexp_nilable_top::calc_nilable method is associated
with the added property, synattr_nilable::my_nilable.  Without this
virtual function, in order to calculate my_nilable for each node, each
node would have to have a flag indicating which regexp_tree type it
was, and a possibly large switch statement on this flag to dispatch to
the correct calc_nilable code.