Re: Problem with packages

[stt@houdini.camb.inmet.com (Tucker Taft)]

Sean kenny (skenny@gifford.co.uk) wrote:

: can anyone tell us why this the following code won't compile
: we keep the following error message 

:  invalid prefix in selected component "working_hold"

: on the indicated lines

: hold_id is defined in the following package which compiles
: ok.

The problem is that hold_id is a private type.
You haven't exported any operations on hold_id, other than "request_work."
If you want next_container and complete to be performed on hold_id,
you will need to declare them in the visible part of "foreman."

You could declare them as "regular" procedures in the visible
part, with an extra "hold_id" formal parameter, and then implement
them in the body of package "foreman" by calling the corresponding
entry of the task type "hold."  You could use a pragma Inline
on these "wrapper" procedures if the extra procedure call overhead
is a serious problem (seems unlikely in this case).

: WITH foreman;
: use foreman;

: PACKAGE BODY gangs IS
: TASK body gang is
:   hold_state : work := more;
:   working_hold: hold_id;
: begin
:   foreman.request_work(working_hold);
:   WHILE hold_state = more loop
:   working_hold.next_container(hold_state);      <----
:   END loop;
:         
:   working_hold.complete;        <------

: end gang;

: END gangs;



: package foreman is

: type work is (more, finished);
: type hold_id is limited private;

: procedure request_work(this_hold : in out hold_id);
: private
: type hold;
: type hold_id is access hold;
: task type hold is
:  entry next_container(state : out work);
:  entry complete;
: end hold;
: end foreman;-- 

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--
-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
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