Re: Change to obscure visibility rule in 9x

[bobduff@dsd.camb.inmet.com (Bob Duff)]

In article <INFO-ADA%94101904360935@vm1.nodak.edu>,
Simtel20 Transfer  <HARBAUGH@ROO.FIT.EDU> wrote:
>Bob Duff writes:
>         2.a   Reason:  The reason for making overloadable declarations with
>         profiles special is to simplify compilation:  until the compiler has
>         determined the profile, it doesn't know which other declarations are
>         homographs of this one, so it doesn't know which ones this one should
>         hide.  Without this rule, two passes over the _specification or
>         generic_instantiation would be required to resolve names that denote
>         things with the same name as this one.
>
>So the compiler has to look at a few hundred bytes of source code twice,
>With today's 8MB and higher PCs that doesn't seem like any problem.

The issue is not an efficiency issue, but a compiler complexity issue.
Forcing the compiler to have a first pass to figure out the type profile
of a given subprogram, then go back and decide which things are
homographs of the subprograms, and then make a second pass, doing
overload resolution on the default expressions, would be a large amount
of extra complexity in the compiler, just to handle something silly that
nobody would really want to write: "function F(X: Integer := F);".

Of course you're right that compilers have plenty of memory to do this
these days.  In fact they probably had plenty of memory in 1983 --
subprogram specs aren't that big.  But compiler complexity causes
compiler bugs -- a Bad Thing.

- Bob
-- 
Bob Duff                                bobduff@inmet.com
Oak Tree Software, Inc.
Ada 9X Mapping/Revision Team (Intermetrics, Inc.)