[fpc-pascal] Converting old pascal written for Pascal/MT+ compiler

[Sven Barth]

Tomas Hajny via fpc-pascal <fpc-pascal at lists.freepascal.org> schrieb am
Di., 4. Apr. 2023, 09:51:

> On 2023-04-04 09:43, Jacob Kroon wrote:
>
>
> Hi Jacob,
>
> >> You don't need to change "var" to "const" - if you want to ensure the
> >> variables to persist in between the function/procedure runs, you need
> >> to move them to the global level, i.e. outside of the
> >> functions/procedures. It is not advisable as a general practice (to
> >> keep all variables globally), because then you might e.g. access the
> >> same variable from multiple functions by mistake, but it would
> >> probably solve your issue. Obviously, you might need to solve
> >> potential conflicts if you use the same variable names in multiple
> >> functions/procedures (e.g. by prepending the function/procedure name
> >> to the variable name or something like that).
> >>
> >
> > I could move them to global scope, and add a prefix to avoid name
> > collisions, but using a "const" section seems more readable to me
> > since I don't need to add a prefix.
> >
> > The wiki page says (https://wiki.freepascal.org/Const):
> >
> > "The declaration const in a Pascal program is used to inform the
> > compiler that certain identifiers which are being declared are
> > constants, that is, they are initialized with a specific value at
> > compile time as opposed to a variable which is initialized at run
> > time.
> >
> > However, the default setting in Free Pascal is to allow const
> > identifiers to be re-assigned to."
> >
> > Then it says there is a flag to make reassigning to a const variable
> > an error. But if I ignore that, it would seem this is just what I
> > need, since this seems to make the variable have a whole-program
> > lifetime, no ?
> >
> > What is the technical downside to using "const", or is it just cosmetic
> > ?
>
> If you read the documentation (wiki or the real documentation in
> PDF/HTML etc.) properly, you don't find there anything saying that
> constants declared locally within functions or procedures are guaranteed
> to keep their modified values across runs of that function/procedure. It
> might behave like that, but you shouldn't rely on it unless it's a const
> on a global level (and then renaming may still be needed in case of
> conflicts).
>

It *is* documented (the remark at the end):
https://www.freepascal.org/docs-html/current/ref/refse10.html#x22-210002.2

Regards,
Sven

>
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