Re: How to Emulate C++ Macro with Static Local Variable?

["Robert I. Eachus" <rieachus@attbi.com>]

tmoran@acm.org wrote:

 > I don't see how
> one might do that without a preprocessor, and I don't see how one could
> (portably) get hold of the Instruction Counter for storage and later
> comparison, in Ada code.

I showed how.  You set it up so that the memoizing function is not 
visible.  All that is visible is a constant record containing a 
subprogram access value.  To make a call you have to make a (variable) 
copy of the constant, and pass that on the call.  Inside the subprogram 
   this is a new call site.  Create a new access value, reset the 
(record) parameter to the new value, do the initial call processing, 
then call the (hidden) value which will be returned.

This second value of the parameter calls the routine which does the 
actual processing sans the initial call code.  This way there is no 
lookup or anything to be done in either case.  Call the initial value in 
the constant, this is the first call from this site.  Call the returned 
value, and this is a subsequent call.  If you want you can either make 
sure that the record containing the access value is passed by reference, 
or add an access discriminant so that inside the first subprogram you 
can cache a list of call sites if you want to.

-- 
                                                        Robert I. Eachus

Ryan gunned down the last of his third white wine and told himself it 
would all be over in a few minutes.  One thing he'd learned from 
Operation Beatrix: This field work wasn't for him. --from Red Rabbit by 
Tom Clancy.