Re: Conditional compilation in Ada?

[Adrien Plisson <aplisson-news@stochastique.net>]

tmoran@acm.org wrote:

>   You can use an "if" statement.
> if Is_Version1 then ...
> else ...
>   If you define Is_Version1 at the top, or in another small package, as
>   Is_Version1 : constant Boolean := True;
> then an intelligent compiler will not generate any code for the impossible
> Is_Version1 = False condition or the if-test itself.  That is, it will be
> identical in effect to C conditional compilation.

will really the compiler not COMPILE the code impossible to reach ? i'm not 
that sure... it will generate no code, and maybe even no check at the entrance, 
but the code is still compiled and checked by the compiler for syntax errors, 
semantic errors and so on.

so, if he has a record:
type Version_1 is record
     Value_Version_1 : Any_Type;
end record

and another version:
type Version_2 is record
     Value_Version_2 : Any_Other_Type;
end record;

then code accessing the Version_1 record will not compile for Version_2, and 
vice versa. the "if" statement is then not an option, and is definitely not 
identical to the C conditional compilation. remember that the C preprocessor 
allows to do conditional COMPILATION, not conditional RUNTIME.

well, before everybody yell, i'm totally aware that this case is typically a 
bad design and should be rewritten using discriminated record. (but some people 
don't quite get it and still write this kind of code, especially in C with #if).

-- 
rien