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From: "kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/114438] Missed constraint F2023:c7108
Date: Sat, 23 Mar 2024 19:56:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114438

--- Comment #2 from kargl at gcc dot gnu.org ---
(In reply to anlauf from comment #1)
> Can you be a little more explicit?
>=20
> If I extend the program as follows:
>=20
>     type(params) :: p
>     p =3D params( 0.1, 2.0 )
>     write(*,*) p
>     p =3D params( 0.1, 2 )
>     write(*,*) p
>=20
> I get with all compilers I have access to (Intel, NAG, Nvidia, flang,
> gfortran)
>=20
>  Not the structure constructor
>   0.100000001       4.00000000=20=20=20=20
>   0.100000001       2.00000000=20=20=20=20
>=20
> This is what I would have naively expected in accordance with "Note 1":
>=20
>   The form =E2=80=99name(...)=E2=80=99 is interpreted as a generic functi=
on-reference if
>   possible; it is interpreted as a structure-constructor only if it cannot
>   be interpreted as a generic function-reference.
>=20
> which gives a precedence to function-reference over structure-constructor,
> making it possible to override the default constructor.
>=20
> Are you saying that one cannot override the default constructor?


I thought C7108 was clear.

  C7108 (R756) If derived-type-spec is a type name that is the same as a
generic
  name, the component-spec-list shall not be a valid actual-arg-spec-list f=
or a
  function reference that is resolvable as a generic reference to that name
(15.5.5.2).

The derived-type-spec is 'params'.

The generic name is 'params'.

The component-spec-list for the derived type in 'p =3D params(3.0,2.0)'
has types of 'real' and 'real'.

The generic reference is 'p =3D params(3.0,2.0)', which resolves to
'default_params'.

'default_params' has an actual-arg-spec-list with types of 'real' and 'real=
'.

Thus, 'params(real,real)' is ambiguous.  Is it the structure constructor
or a generic function reference?

Note, you cannot use keywords as the components of the derive
type 'params' are 'x' and 'y', and the dummy arguments for=20
'default_params' are also 'x' and 'y'.

Finally, 'p =3D params(3,2.0)' is a structure constructor, because the
generic interface does not include a function with types of 'integer'
and 'real'.  Thus, here, this is not a function reference.  It must
be a structure constructor.  The rules of intrinsic assignment are
now in play, and 'params(3,2.0)' is treated as 'params(3.0,2.0)'=20
after type conversion.

Of course, I could be wrong.=