Re: type conversion

[Pascal Obry <pascal@obry.net>]

Le samedi 11 octobre 2014 à 22:57 -0600, Shark8 a écrit : 
> Almost,
> 
> Subtype Integer_String is new String
>    with Dynamic_Predicate => Integer'Value( Integer_String ) in Integer
>                              or else raise Constraint_Error;


I don't see the point of the "or else" part. The exception
Assertion_Error will be raised if the first part "Interger'Value .. in
Integer" is not True anyway.

To control the message or the exception to be raised one can use the
Predicate_Failure aspect:

subtype Integer_String is new String
   with Dynamic_Predicate => Integer'Value (Integer_String) in Integer,
        Predicate_Failure => "not an integer string";

or

subtype Integer_String is new String
   with Dynamic_Predicate => Integer'Value (Integer_String) in Integer,
        Predicate_Failure => 
          raise Constraint_Error with "not an integer string";

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