Re: Min/Max attribute makes promises it can't keep

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

On Sat, 1 May 2010 00:42:53 -0500, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:1p28brlj9yc3k$.1nv0ey1aadvoi$.dlg@40tude.net...
>> On Wed, 28 Apr 2010 16:07:24 -0500, Randy Brukardt wrote:
>>
>>> As for the initial concern about giving a subtype name, in the case of
>>> literals you have to give one somewhere (since a literal can be of many
>>> different types, and the results can vary depending on the type used --  
>>> not
>>> for 'Length, but for 'Last and most other properties).
>>
>> No problem, Ada supports overloading in the result type. E.g. abs (-1) is
>> OK.
> 
> That doesn't help. Consider:
> 
>     type My_String is array (Natural range <>) of Character;
> 
> Now, if you wrote:
> 
>     "ABC"'First
> 
> The answer depends on whether the type of the prefix is String or My_String, 
> but the type is Integer'Base in both cases. No amount of overloading will 
> help.

How is that different to:

   package P is
      function ABC return String;
   end P;
   package Q is
      type My_String is array (Natural range <>) of Character;
      function ABC return My_String;
   end Q;
   use P,Q;
   ...
   ABC'First; -- Ambiguous

> The language does not want the compiler to have to list out all of the 
> possible types for a string literal, figure out the appropriate bounds for 
> all of them, take all of the ones with the appropriate index type, and then 
> allow the attribute if the answer is the same.

That would be silly, of course. But it is not what I meant. Attribute
should be an overloaded operation as any other. If the expression happens
to be ambiguous there are language means to specify what it is.

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