RE: Could RPG become quasi-immune to level checks (was: Are level checks still useful?)

[Åke Olsson <ake.olsson@xxxxxx>]

It is imho possible to code level-check-immune RPG. That is if you use SQL for access and also always list the columns you select (not "select *") fields can be added (or dropped for that sake) from the table without disturbing the program.


Med vänlig hälsning / Best regards

Åke H Olsson


-----Original Message-----
From: Jeff Crosby [mailto:jlcrosby@xxxxxxxxxxxxxxxx] 
Sent: den 1 november 2012 17:43
To: RPG programming on the IBM i / System i
Subject: Could RPG become quasi-immune to level checks (was: Are level checks still useful?)

> The reason you don't have level checks in PHP (and similar 
> environments) is because they don't have hard-coded from/to positions 
> in fields in the record.  When you compile an RPG program, the 
> compiler reads the external definition, and hard-codes the from/to 
> positions of fields in the record into the program.  You have to 
> recompile for it to update these -- and therefore, level checks are an 
> important safeguard. Without them, if the file changes, you'll end up 
> reading (or worse, writing) incorrect data at incorrect places in the record, causing a big huge mess.

Scott's post got me thinking.

Theoretically, could RPG be enhanced such that the from/to positions are _not_ hard-coded at compile time?  Instead, based on field name (whether renamed or not), the from/to positions would be established at run time.
 If so, one would also have to code updates properly, i.e., either  via "Update RecordName %Fields(blah:blah:blah);" or making sure the O specs have no end position.

Even though I have absolutely no experience whatsoever in compiler writing (and don't want any), I can imagine how this would fundamentally affect the compiler.


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Jeff Crosby
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