Structured exception information

[Maciej Sobczak <no.spam@no.spam.com>]

Hi,

Consider an object created by a constructor function:

X : My_Type := My_Constructor(Some_Parameters);

My_Type is Controlled_Limited to ensure control over initialization and 
finalization. The idea of constructor function is to prevent the 
existence of objects that are not yet initialized, half-baked, in a bad 
state, etc. If the object exists, it's ready for use.

If there are problems during the execution of the constructor function, 
the exception is raised, so that there is no X object in a bad state.
How can I pass some error information from the constructor function out, 
so that it's used when the exception is handled?
Obviously, some message can be attached to the exception occurence, but 
it doesn't scale well - I might want to pass some more data, possibly 
structured (some error code, some reason code, some timestamp, some 
whatever else, ...).

Yes, I'm asking for "throwing objects", in the C++ parlance.

How to do this in Ada?
If I cannot - how to solve this design problem?

BTW - How can I ensure in a general way that the constructor function 
must be used to initialize the object, otherwise compile-time error is 
reported?
If I make My_Type a discriminated type (so that the discriminant value 
is used in the default initialization), does it limit anything, like 
constructor parameter types?

-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/