Re: ML-like alternatives to out parameters for functions

[Preben Randhol <randhol+news@pvv.org>]

Mark Lorenzen wrote:
> There has lately been some discussions about Ada's missing
> capabilities for specifying out parameters for functions. Apparently
> this is a needed feature and an AI (AI-323) has been issued.
> 
> An out parameter can be used when the validity of the result of
> evaluating a function is not always well-defined. For example:
> 
> function Calculate (Argument : in AT; Result_Valid : out Boolean) return RT;
> 
> 
> Use of the function could be as:
> 
> Result := Calculate (Arg, Valid);
> if Valid then
>   .. do stuff with Result ..
> else
>   .. handle error ..
> end if;

Or you could do 

function Calculate (Argument : in AT; Result : out RT) return boolean;

Use of the function could be as:

if Calculate (Arg, Result) then
  .. do stuff with Result ..
else
  .. handle error ..
end if;

-- 
�Don't use C;  In my opinion,  C is a library programming language
 not an app programming language.�  - Owen Taylor (GTK+ developer)

Use Ada 95, a free language. More info at http://www.adapower.com/