Re: Ada -vs- GNAT

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Richard Riehle <richard@adaworks.com> writes:

> A long time ago, in a far away place called Data Processing Land,  we had
> languages such as COBOL, and compiler publishers addressed specific
> user and platform needs by adding new reserved words and other features
> to the language.    ACT appears to be taking a more responsible approach
> by 1)  not adding new features to the language,  2) tailoring their compiler
> through the use of pragmas and attributes as authorized by the ALRM, and
> 3) making it possible to avoid these additions by configuration pragmas.
> This seems pretty reasonable to me, and I am, as you all know, a pretty
> unreasonable person.

It seems to me that (3) is the key point.  It doesn't really matter very
much whether language extensions are new syntax or new pragmas and
attributes.  If you use compiler-specific functionality, you damage your
portability either way.  The fact that the RM authorizes certain kinds
of language extensions doesn't change this fact.

For example, if you make heavy use of 'Unrestricted_Access to make
downward closures, you're going to have a lot of trouble porting to a
compiler that doesn't support 'Unrestricted_Access.  If the same feature
were provided with syntax, it would be no harder and no easier.
The important thing is that you can run the compiler in a mode where it
forbids such extensions.

- Bob