Re: Ada exceptions. unchecked?

[Dale Stanbrough <dstanbro@bigpond.net.au>]

Darren New wrote:

> For a sloppy and imprecise example,
>   application's main calls file_open_dialog,
>     file_open_dialog calls gui_button_handler
>       gui_button_handler calls application's load_file
>         application's load_file calls Java's read, which throws EOF_error.
> 
> At this point, the application's load_file has to get the error back to the
> application's main routine to be handled. But the gui_button_handler doesn't
> declare that it can throw EOF_error, because the button hasn't anything to
> do with files. So the normal technique is to create a new unchecked
> exception and pass the checked exception in the constructor, then throw
> that, then catch it in the main routine and unwrap it.

Note that this problem would also apply if exceptions had
to be declared in a subprogram, and those subprograms were used
in a generic.

For example I have a convenience generic to iterate over each line
of a file - you pass a procedure that does the work on each line.
Clearly the generic can't know what exceptions the procedure could
generate.

Dale