Re: Ada 2012: In-out parameters for functions

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 01 May 2013 21:58:36 +0200, Yannick Duchêne (Hibou57) wrote:

> Le Wed, 01 May 2013 21:37:43 +0200, Dmitry A. Kazakov  
> <mailbox@dmitry-kazakov.de> a écrit:
> 
>> On Wed, 01 May 2013 21:04:03 +0200, Yannick Duchêne (Hibou57) wrote:
>>
>>> In/out (both way) parameters may be another story, and may more suggest
>>> this is a procedure and not a function,
>>
>> function Read (Stream : in out Root_Stream_Type) return String;
> 
> :D
> 
> This is more a procedure than a function (it either won't return the same  
> the next time invoked with the same argument or either the argument can  
> never be considered to be the same as it use to be any‑more),

Surely it will. Same argument means same value and the value of a stream is
its state. If the stream is in the same state the function will return same
result.

> and a  
> function construct is used only because it is preferable to return an  
> unconstrained type

Not only. Functions are used when there is a dedicated result/effect which
is used as an input for another routine or language construct.

> That's a good example of how a construct may not always match the intended  
> semantic;

The semantics [in the context of program design] of a function and
procedure are exactly same, it is called "subroutine."

> I feel `function` and `procedure` in Ada means something at the  
> implementation level more than at the intention level, even if many times  
> both matches as gloves and hands.

Ada 83 confused function as a syntactic form of a subroutine with pure
function. Allowing in/out arguments resolves that only partially. Pure
functions (of different purity levels) are still needed.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de