Re: File with LikeRec Data-Structure Template -vs- ExtName Data-Structure Template

EXTNAME simply retrieves the structure of the file at compile time...

So no, you don't have to re-compile the program unless you have a
requirement to pick up the new definition..

One such use case, you have _dynamic_ SELECT * SQL statement...

A static SELECT * isn't a problem given the way the pre-compiler works...

Though SELECT * in production is generally a bad idea.

As far as an END-DS, jon covered the reason...EXTNAME allows you to add
fields to the DS...

dcl-ds myds extname(mytable);
extraFld1 char(10);
extraFld2 char(15);
end-ds;

Assuming MYTABLE has 5 columns, the myDS structure above will have 7
subfields...

Charles

On Wed, Oct 16, 2019 at 10:43 AM Robert Jacobs <robertjacobsit@xxxxxxxxx>
wrote:

That's a great explanation. Thanks, Jon!

Are you also able to verify that, when using the extName keyword, a change
to the physical file would not require a re-compile of the program, unless
the change was to a field explicitly referred to?

Finally, I do still wonder why the end-ds is required for an extName
data-structure, but not a likeRec data-structure. It's not straight
forward what the issue is when encountered in RDi (when you leave out the
end-ds), so it took me a bit to even realize that's what was causing a
problem. I also had to account for extName template not being qualified (I
expected the template keyword to make the data-structure qualified
automatically) as opposed to the likeRec template being qualified by
default (a result of the likeRec keyword), but that's just a nitpick.



On Wed, Oct 16, 2019 at 10:11 AM Jon Paris <jon.paris@xxxxxxxxxxxxxx>
wrote:

I can't think of any real advantage to using the file approach - unless
you plan on passing the file as a parm - which is primarily what

templated

files are for.

The ExtName approach also has the advantage that additional fields and/or
redefinitions can be added to the DS. A LikeRec cannot be used in that

way.

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