Re: Reference Semantics

[billwolf@hubcap.clemson.edu (William Thomas Wolfe,2847,)]

From article <10322@umn-cs.CS.UMN.EDU>, by stachour@umn-cs.CS.UMN.EDU (Paul Stachour):
>   I'm for reference semantics.  They are natural, efficient, and
> don't force this explicit-pointer "junk".  But let's make sure
> what we can do with them in today's environment before we ask
> Ada 9X to mandate them.

    OK, we're sold on the benefits of reference semantics.  Let's assume
    that "in out" parameters are always passed by reference.  Now why
    should it be impossible for the programmer to choose pass-by-value,
    as in "in" and "out" modes?  

    (BTW, a good compiler could eliminate the copy in many cases by
    proving to itself that there is no attempt to modify the "in" parameter 
    and therefore just passing it by reference anyway.  Such compiler analysis 
    is necessary because programmers frequently want to use "in" mode 
    just to assure the procedure's users that the parameter will not 
    be modified.  But sometimes the local copy is modified, and the
    copy then becomes something that would have had to be done anyway.
    To force an explicit copy would then reduce program readability.)