Re: parameters - const, value, reference

["Richard B Baird" <rbaird@xxxxxxxxxxxxxxxxxxxxx>]

Scott,

ding, ding, ding!  thanks.  while the light in my head is not 100 watts
yet, it's at least 70.

<snip>

> > 1. const means you are passing the value and don't expect it to change
or
> > need it to be returned when the function ends.

> const means you're passing by reference, not value.  Otherwise, you're
> right.

right - i saw that after I posted it - 'value' was misleading.

<snip>

> What about CONST, you say?  Well, CONST is a different way of saying
> "read-only reference."   The parameter is passed by reference, but you're
> not allowed to make any changes to it.  Thus, "read-only."

so, you're saying that if you pass a parm 'const', changing that variable
locally is verboten.

ok then...

<snip>

>    If you need to change your local copy only, or if the variable is
>    smaller than 16-bytes long, pass it by value.
>    If you don't need to change it at all, and it's larger than 16-bytes
>    long, pass it by "read-only reference", aka CONST.

if you have a rather large string that you might want to change locally,
does it matter whether you pass by value and change in-line, or
const/reference and move it to a locally defined variable for manipulation
- 6 of one, .5doz of another. you are still moving the data.

>    When calling a PROGRAM (as opposed to a procedure) you MUST pass by
>    reference.   CONST is allowed, as that is still by reference.

define program:  it has a 'main'?

do you now prototype all of your new programs instead of using *entry
plists?

does that mean all of your other rpg and CL programs that call them use
callp instead of call?

>    When passing by either VALUE or CONST the compiler knows that you
>    will not be changing the variable, and therefore will automatically
>    insert code to convert from one variable type to another, or allow
>    you to use expressions, etc as appropriate.

elaborate on the phrase 'insert code to convert from one variable type to
another'.  I understand the using expressions part - but I assumed that the
expression would have to resolve to the same type of data as that the
parameter is expecting:

(%len(x)+1) would resolve to numeric data, (although i suppose the proc
could be expecting string and still be able to use this), and

(%trim(str1) + %trim(str2) would resolve to alpha, and unless there are
only numerics in the strings, couldn't be passed to a numeric parm.

is that what you mean by 'converting' variable types?  can you give me an
example of other types of variables that could be 'converted'? (pointer,
%addr(), date, binary, etc.)

> Hope that helps.

very much!

thanks,

Rick