when My_Type is an indefinite subtype.

type My_type (<>) is ... for example

Then, when you declare an object of that type you must provide an
initialization expression (a constructor call !).

Maciej Sobczak a écrit :
> 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/