Request for comment: Character substring lengths

[Tobias Burnus]

Hi,

FX Coudert wrote:
> Doesn't the following alone fix problems?
>> +    /* Set the length to the substring length, if known at compile
>> time.  */
>> +    if (ref->u.ss.start->expr_type == EXPR_CONSTANT
>> +       && ref->u.ss.end->expr_type == EXPR_CONSTANT)
>> +      {
>> +       mpz_sub (ref->u.ss.length->length->value.integer,
>> +                ref->u.ss.end->value.integer,
>> +                ref->u.ss.start->value.integer);
I played around a bit more. This does not work: If I use
  p => s(2:3)
then len(s) is 2. One could use a new ref->u.ss.ss_length instead of
ref->u.ss.length, but this looks clumsy. In addition, it won't work for
symbols as they only have ts.cl->length -- and for substrings this is
zero. One could copy ref->u.ss.ss_length to the symbol. Is this the
right approach?

Tobias Schlüter wrote:
> Indeed, I found about this recently when I prepared my last series of
patches.
> I think I wrote something about this in one of my patch submissions

You don't mean the following, do you? Or do you?

> I just had the following idea for a beginner's project:  we could get
> rid of these double-checks by having a global gfc_charlen
> gfc_empty_cl, whose length member would be initialized to NULL
> (happens automatically, as it's in global storage).  Then, instead of
> zeroing ts.cl if the charlen is not known, we would make it point to
> &gfc_empty_cl.  Then ts.cl would never be NULL, and ts.cl->length ==
> NULL would be necessary and sufficient for an unknown length. 

But I don't see how it would help.

Tobias