Re: Don't we already have a 'Valid? (was Re: Unchecked_Conversion...)

[dst17!mab@ford-wdl1.arpa (Mark A Biggar)]

In article <26q196INNl1t@umbc4.umbc.edu> berman@umbc.edu (Mike Berman) writes:
>The prior discussion on unchecked_conversion has quite adequately
>explained why the code I excerpted operates the way it does. The result
>of the unchecked_conversion makes the program erroneous if it is not a
>valid member of the target type.
>The real question is why does the "type_mark" form of the "in" operator
>exist? Most people use "in" solely for checking ranges within a scalar
>type, but it is defined to operate on _any_ type. Since it can't be used
>to check the results of unchecked_conversions, then why is it defined
>for nonscalar types?

Well in 9x, with tagged types it is useful for asking if a classwide
variable is of a given tagged type.

>And, as the subject line suggests, why not use the already-defined
>syntax for the "in" operator _instead_ of adding the 'Valid attribute?

The complier is allowed to optimize way an "in" operator, but is specifically
forbiden to touch a 'VALID, otherwise they should act the same.

--
Mark Biggar
mab@wdl.loral.com