Re: Q: type ... is new String

["J-P. Rosen" <rosen@adalog.fr>]

Le 04/06/2012 09:48, Yannick Duchêne (Hibou57) a écrit :
> Good idea. I did not consider this one, may be due to the natural
> tendency of deriving from an already existing type with similar meaning.
Which is very common, and to my taste, not a good idea.

One of the unique features of Ada is the ability to define your own
types that match your needs from scratch, without hooking them to some
predefined "magical" types with special properties, as happens in most
other languages.

Integer is an integer type like any other, String is an array type like
any other, etc. No reason to derive from them, but there are good
reasons not to. For example, if you define:
   type Int is new Integer range 1..10;

you inherit (by default) the representation of Integer, presumably 32
bits. And you can't define this way a type /wider/ than integer. If you
write:
   type Int is range 1..10;

the compiler chooses the most efficient implementation, and there is not
limit other than the capabilities of the machine.

-- 
J-P. Rosen
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