Re: question on exceptions

[gauthier@unilim.fr (Michel Gauthier)]

In article <E090uD.Kx6@tip.nl>, michiel.perdeck@cmg.nl wrote:

>>  [...]
>>  
>>  Questions:
>>      Unlike an exception in C++, an Ada exception cannot carry any
>>  extra information besides it's own name. [...]

Ada _can_ do this :
 - directly, in the case of String values,
 - indirectly, for every type with functions similar to
    the Image and Value attributes.

Attaching a String to a raise is a basic operation available
in the Ada.Exceptions predefined package.

For things other than String values, you can attach the Image
of what you want to attach. Inside the exception handler, you
can extract the message, and take its Value, which gets back
the initial value.

Caution : this works only if you can control that all raises are
correctly attached. Therefore, either you restrict such uses to
non-resusable parts, or you handle Constraint_Error possibly
caused by the back-parsing of the message.

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