Re: Not grasping concept

["Paul Tuohy" <tuohyp@xxxxxxxxxxxxx>]

Hi Tim,

You are assuming that a prototype is like a PLIST - it isn't.

Look at it this way:-

- A PI definition is the equivelent of a *ENTRY PLIST.
- The compiler needs to validate any PI definition and any CALLP style call
(either using a CALLP operation or a BIF style call, as in your example).
- To do this validation, the compiler needs a template to validate against -
that is what the prototype is for.

To get the idea of this - try removing the field names in the prototype and
recompiling - it will compile just fine, because the prototype is not
defining anything that is used by the program - only by the compiler.

HTH

Paul Tuohy


----- Original Message -----
From: "Tim Kredlo" <TKredlo@xxxxxxxxxxxxxxxx>
To: <RPG400-L@xxxxxxxxxxxx>
Sent: Wednesday, October 15, 2003 1:10 AM
Subject: Not grasping concept


> Please help!
>
> I am having a VERY difficult time grasping the concepts behind
> prototypes/return values/procedure interfaces.
> Here is what I understand the recommended process to be:
>
> Define a prototype for the subprocedure (TESTSP). and store it in the
> source PROTSP.
>
> It will return a numeric field 15 characters long with 3 decimals
>  and it requires 3 numeric input parameters.
> D TestSP        PR            15S 3
> D Unit                             2S 0
> D Qnty                            8S 0
>   D Long                            3S 0
>
> So far, so good.
>
> Now I am going to write the subprocedure itself.
> H NOMAIN
> // Include the prototype
> /Copy PRODLIB/QRPGSRC/PROTSP
> Still OK. BUT then:
> // Define the procedure interface
> D TestSP      PI
> D Unit                             1A
> D Qnty                            8S 0
> D Long                            3S 0
> Why is this necessary?
> Didn't the included prototype already declare these fields?
> Wasn't that the purpose of the prototype?
>
> // Declare the field to be returned:
> D Footage                     15S 3
> Why is this necessary?
> Didn't the prototype already declare the return value
> type/length/decimals?
>
> /Free
> //Calculate the return value
> Footage = Unit * Qnty * Long;
> // Return the calculated value
> Return Footage;
> /End-Free
>
> I must be missing some very basic concepts, because I would have thought
> that the following was ALL that SHOULD be necessary for subprocedure
> TestSP:
>
> H NOMAIN
> // Include the prototype
> /Copy PRODLIB/QRPGSRC/PROTSP
> // Calculate and return value
> /Free
> TestSP = Unit * Qnty * Long;
> /End-Free
>
> No PI defined - already did that in the prototype.
> No "Return" variable defined - use the subprocedure name. Type, etc.
> defined on prototype PR line.
> No Return statement required - stated in prototype that the subprocedure
> returns a 15S 3 variable.
>
> Please - what am I missing?
> Where can I go to get an explanation as to WHY I need to add
> what I consider (obviously incorrectly) unnecessary coding?
>
> OR: Am I coding things here that ARE unnecessary?
>
> Thanks in advance for any help.
>
> Frustrated, uninformed, and confused (but only in my mind),
>
> Tim Kredlo
>
>
>
>
>
>
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