Re: [Patch, Fortran, OOP] PR 49638: [OOP] length parameter is ignored when overriding type bound character functions with constant length.

[Janus Weil <janus at gcc dot gnu dot org>]

>> It is wrong to assume that expressions are unequal because we cannot
>> prove they are equal, with all the limitations that we currently
>> have. ?This will introduce rejects-valid bugs.
> In the PR at
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49638#c8
> I quote the standard:
>
> 4.5.7.3 (type-bound procedure overriding) has:
> • Either both shall be subroutines or both shall be functions having the same
> result characteristics (12.3.3).
>
> 12.3.3 (Characteristics of function results):
> If a type parameter of a function result or a bound of a function result array
> is not a constant expression, the
> exact dependence on the entities in the expression is a characteristic
>
>
> So the standards is more restrictive than expression values being the same. It
> requires _the exact same dependence on the entities_. My reading of this is
> that 3*(x+1) vs 3*x+3 is right to be rejected, same for (a+b)+c vs a+(b+c).
> The only worrying case that I see is the one you pointed out: a+b+c vs c+b+a
> (without brackets).

Huh, I don't see what is so different between

1) 3*(x+1)   vs  3*x+3   and
2) a+b+c  vs  c+b+a

In both cases the expressions look different at first sight, but can
be transformed into each other mathematically. So I'd say they are
mathematically equivalent, although the spelled-out representations of
these expressions differ.

The question is how you interpret the standard's formulation of "exact
dependence on the entities in the expression". Naively I would have
taken this to mean the *mathematical* dependence (which can be
represented by different actual expressions). But I'm fine with your
interpretation, too, which will make life even easier for us.

Cheers,
Janus