Re: Noob question: universal_integer type

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

On Sat, 22 May 2010 13:04:03 GMT, Duke Normandin wrote:

> On 2010-05-22, Niklas Holsti <niklas.holsti@tidorum.invalid> wrote:

>> Perhaps it is also worth mentioning that Ada does have a way of 
>> explicitly indicating the type to be chosen for a literal, by 
>> "qualifying" it with a type name. This can be necessary to resolve 
>> overloaded operation names. For example, assume that you define two 
>> integer types:
>>
>>     type Apples is range 0 .. 20;
>>     type Ants is range 0 .. 1_000_000;
>>
>> and then define a procedure "Eat" for each type, with different content 
>> for eating apples and for eating ants:
>>
>>     procedure Eat (Items : Apples) ... end Eat;
>>
>>     procedure Eat (Items : Ants) ... end Eat;
>>
>> A call of Eat with a literal parameter, for example Eat (17), is then 
>> ambiguous (and the compiler will tell you so). To show if you are eating 
>> apples or ants, you qualify the literal with the type name and an 
>> apostrophe, as in
>>
>>     Eat (Apples'(17));
>>
>> for eating 17 apples, or
>>
>>     Eat (Ants'(17))
>>
>> for eating 17 ants. Since the type of the parameter is now explicit, the 
>> compiler knows which procedure Eat is to be called.
> 
> I love it! and the compiler would choke with an "out of bounds" exception if
> you called Eat (Apples'(25)); - if I understand the Coronado tutorial
> correctly. Thanks for the input...

Yes, the Constraint_Error exception. But note, this is OK:

   Eat (Apples'(25 - 10));

This is another reason behind universal types. You can perform computations
on them ignoring constraints of the particular type.

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