RE: Advantages of RPG

While I agree with Joe that RPG's SELECT op-code is nice to have, it should be pointed out that other
languages ( or RPG itself) simply use IF - ELSIF - for this type of logic.

// Opcodes 01 and 02 don't need authorization
If OPCODE = '01';
DoOpcode1();
ElseIf OPCODE = '02';
DoOpcode1();

// Opcode 10 needs authorization
ElseIf not Authorized();
SendError('Not Authorized');
ElseIf OPCODE = '10';
DoOpcode10();

// Bad opcode
else;
SendError('Bad Opcode');

Endif;


One could argue that having a switch type statement instead of the RPG select is useful due to the
more structure provided.
//pseudo RPGLE
switch opcode;
when '01';
DoOpcode1();
when '02';
DoOpcode2();
when '10';
if not Authorized();
SebdError('Not Authorized');
Else;
DoOpcode10();
Endif;
Other;
SendError('Bad Opcode');
Endsw;

Personally, I wish RPG would take a clue from SQL and support both formats.

Select (test) when....
And
Select when (test1)....

Or give us a separate switch op-code.


Charles Wilt
--
Software Engineer
CINTAS Corporation - IT 92B
513.701.1307

wiltc@xxxxxxxxxx

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Joe Pluta
Sent: Monday, June 23, 2008 12:23 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: Advantages of RPG

Doug Palme wrote:

your statement of "perhaps the best
implementation ever..." are you referring to the SELECT statement
specifically or the group as a whole? The reason I ask is that
SELECT-ENDSL is the same as SELECT CASE-END SELECT is it not?

If I am off the mark on this, please feel free to correct me.

Not a correction so much as a clarification. Most implementation of
CASE logic have actually been variations on the SWITCH statement. The
concept of a switch is that you have a single variable, and then you
execute logic based on the contents of that variable.

switch (a) {
case 1: doSomething1();
break;
case 2: doSomething2();
break;
default;
doSomethingElse();
}

SELECT on the other hand was much more a derivation of the old CASE
construct in RPG, where you could compare any two variables. And in
RPG, a combination of SELECT and procedures is incredible:

SELECT;

// Opcodes 01 and 02 don't need authorization
WHEN OPCODE = '01';
DoOpcode1();
WHEN OPCODE = '02';
DoOpcode1();

// Opcode 10 needs authorization
WHEN not Authorized();
SendError('Not Authorized');
WHEN OPCODE = '10';
DoOpcode10();

// Bad opcode
OTHER;
SendError('Bad Opcode');
ENDSL;

The code above is just stunningly simple for client/server programming.
I used this all throughout the RSDC Scheduler application and I was able
to create new servers in minutes. The fact that the WHEN can be as
complex as you need it, or even execute a subprocedure (which in turn
could call another program!) makes this one of the very best opcodes
ever designed for procedural logic.

Joe

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