Re: Constants in RPG

On Wed, Apr 1, 2009 at 3:54 AM, David FOXWELL <David.FOXWELL@xxxxxxxxx> wrote:

Hi people,

I'd like some comments concerning the use of constants. I've been asked to prepare a presentation to the team for a discussion on good coding practices, as the boss is getting tired of seeing this sort of thing :

http://systeminetwork.com/article/rpg-iv-style-21st-century

 * Global figurative constants
 *   Type relation = aunt
D gA          C            'A'

 myRelation = gA;

That's just plain silly. There's two reason to use named constants
instead of a hard coded literal or "magic number"
1) To give it a useful name that tells what the value means, ie. AUNT,
UNCLE, HOURS_PER_DAY
2) If the literal value ever needs to change there's only one place to
change it.

gA above doesn't meet objective #1.

Now, I'd have written :

D gAUNT       C            'A'

D gUNCLE      C            'U'

 myRelation = gAUNT;

Much better.

I tend to tie the constant value to the field:
d RELATION_AUNT
d c 'A'
d RELATION_UNCLE
d c 'U'

// Class Code 02: No Data
d SQL_STATE_NO_DATA...
d c '02000'
d SQL_STATE_NO_MORE_RS...
d c '02001'

Some questions :

I would normally not use a commentaire at the declaration of a constant. What do you think?

I'm sure there's exceptions to prove the rule, but by using an
appropriate name, you should never need a comment for a constant
declaration or a variable declaration. Added a comment for a group of
declarations is another matter, as in my example above.

We use a prefix g to indicate a globally defined constant, and w for a locally defined one. When would you locally define a constant in a sub procedure? I think it's nice to be able to see the definitions close to the calculation specs, but isn't a constant almost always global?

Unlike variables, there's no benefit to declaring a constant locally.
Most of my end up declared in a /COPY file with prototypes and
template declarations. I also have a STDCONST copy member that
contains constants that could be used in many places, HOURS_PER_DAY,
DAYS_PER_WEEK, ect. Any remaining get declared globally for the
module.

One could argue that a constant should never be local. As that would
allow you to have different definitions of it in different procedures.
Which defeats the purpose of a constant.

What is meant by figurative constant? I thought it was one with a fixed value like *BLANK.

You are correct, from the manual, "Figurative constants are implied
literals that allow specifications without referring to length:"

HTH,
Charles