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Wed, 27 Sep 2017 23:16:23 +0000 Received: from DM5PR11MB1930.namprd11.prod.outlook.com ([10.175.88.7]) by DM5PR11MB1930.namprd11.prod.outlook.com ([10.175.88.7]) with mapi id 15.20.0077.016; Wed, 27 Sep 2017 23:16:23 +0000 From: Bill Long To: Van Snyder , fortran standards email list for J3 CC: sc22wg5 Subject: Re: (j3.2006) (SC22WG5.5973) Generic programming examples Thread-Topic: (j3.2006) (SC22WG5.5973) Generic programming examples Thread-Index: AQHTN8zlyFkA0qmUlEueg/v0cn0vWKLJXakA Date: Wed, 27 Sep 2017 23:16:22 +0000 Message-ID: References: <20170927201113.6D137358742@www.open-std.org> In-Reply-To: <20170927201113.6D137358742@www.open-std.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=longb@cray.com; x-originating-ip: [136.162.2.1] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR11MB1930;6:CTFDAYtk1J8j6D85CTk+zz6iAae0vOeoMFxmgXRHVOnSv1fDjFaWcoH5Tk5/DfGiJriGSwMmsVkjCpQWaFek61PUa4cHUckuiB5iNFY4D8xxngWQvG2I0e3Xuo8NxLo4hMr0mLJ5Ftc7GgxO+oMq1B1yq/fFqqiZAqu2KQCKN/xgNBaTHmbOS4TPCOaimf70qZaAcLiLnudpBfj7xOO2r3oIVl3QDkrLsmOfP4SnEyemvN2LgCqqI1jiUsp1uYdVMuQj67+3s8Fz9J7wcF7mfBkdqhgnKauUEhIjWt6dpJJGKhDaodH8slIwIvlX0g55EGyumFRXZbkTJH1C2C5Fdg==;5:/+8szUHxvtGjPZpex+BJG26+M4y8bUZRsXZtH3ZV7bAWdvqQvXFz+e47pr9TrFKNIRPffmVTtQ5CxHRDAvjvNH3hnzR4M+yaxIOQsZoLk6QDmxFWVqLZtoi3TzlgJH6hFEL2nmOFEo9N3tSFYKBC2Q==;24:Ug1cwJKRrb6Tuw/PG8BJj00MbyP6ac4lkb/ox+I4QxFOnqXDXHQPn96zv2x5ICjL00/sqmrpjMdDr8aG0oo2jX7ed3bZWofcfSdZBJvBimE=;7:7LFZAbZWuvQUzoaUvDm7JqVcHR0pJeYXkEvElAozAIuq8+kpsBguEuVYBp+iziOfcnP99ph3QSmJT5UsPwfopTjSLs9OEX/wyowS2jaQcSv6UvYLLGb2jvMoE2iGW3poUC9TRjV1iT7RCM5RCzEU72IvwnRL9YPEjao1chV74jNYSiGd8SST/PM/QlXUeyBa7q+XsRzcYn9LQSnuderxdgYXy387LSHJb5bLcQxmN3E= x-ms-exchange-antispam-srfa-diagnostics: SSOS;SSOR; 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And the = complication of type-bound procedures seems unnecessary as well. Simple, c= lean code is almost always better.=20 Cheers, Bill > On Sep 27, 2017, at 3:11 PM, Van Snyder wrote: >=20 > Consider a module for spline interpolation: >=20 > module Splines > type :: Coeffs ( RK ) > integer, kind :: RK > real, allocatable :: A(:), B(:), C(:), D(:) > contains > procedure :: Eval_D, Eval_S, ... > generic :: Eval =3D> Eval_D, Eval_S > ! And more procedures to compute A, B, C, D, etc. > end type Coeffs > integer, public, parameter :: DK =3D kind(0.0d0), SK =3D> kind(0.0e0) > contains > subroutine Eval_D ( C, X, Y ) > integer, parameter :: RK =3D dk > class(coeffs(rk)), intent(in) :: C > real(rk), intent(in) :: X > real(rk), intent(out) :: Y > include "Eval_Body.f9h" > end subroutine Eval_D >=20 > subroutine Eval_S ( C, X, Y ) > integer, parameter :: RK =3D sk > class(coeffs(rk)), intent(in) :: C > real(rk), intent(in) :: X > real(rk), intent(out) :: Y > include "Eval_Body.f9h" > end subroutine Eval_S > .... > end module Splines >=20 > Now I need single, double and Q-precision splines: >=20 > use Splines, only: Coeffs, DK, SK > integer, parameter :: QK =3D selected_real_kind ( 1 + precision(1.0d0) ) > type(coeffs(dk)) :: C_D > type(coeffs(sk)) :: C_S > type(coeffs(qk)) :: C_Q > real(dk) :: Y_d > real(sk) :: Y_S > real(qk) :: Y_q > call c_d%eval ( 1.5_dk, y_d ) > call c_s%eval ( 1.5_sk, y_s ) > call c_q%eval ( 1.5_qk, y_q ) >=20 > Notice that Splines doesn't define a Q-precision Eval_* subroutine, and > Coeffs doesn't provide a generic binding for one. So the code won't > even compile. Generic resolution fails because there is no Q-precision > generic to match c_q%eval. This is a problem if all you have for your > spline library is .o and .mod files, and the company that provided it no > longer exists to give (or sell) you source to upgrade to your > requirements. >=20 > This is what Richard Maine warned about twenty years ago -- when Ada > generic packages had already been in use for fourteen years, and had > been part of the Ada requirements since before FORTRAN 77. >=20 > Let's do it using a parameterized procedure without a parameterized > module (the syntax extensions should be obvious): >=20 > module Splines > type :: Coeffs ( RK ) > integer, kind :: RK > real, allocatable :: A(:), B(:), C(:), D(:) > contains > procedure :: Eval_D, Eval_S, ... > generic :: Eval =3D> Eval_D, Eval_S > end type Coeffs > integer, public, parameter :: DK =3D kind(0.0d0), SK =3D> kind(0.0e0) > procedure :: Eval_D =3D> Eval ( dk ) > procedure :: Eval_S =3D> Eval ( sk ) > contains > subroutine (rk) Eval ( C, X, Y ) > integer :: RK > class(coeffs(rk)), intent(in) :: C > real(rk), intent(in) :: X > real(rk), intent(out) :: Y > ... (don't need Include "Eval_Body.f9h") > end subroutine Eval > end module Splines >=20 > Now I need single, double and Q-precision splines: >=20 > Assume I got only .o and .mod files from a vendor, so I don't have > source to upgrade. So first, I need to extend Coeffs and define a > Q-precision evaluator: >=20 > module Splines_Q > use Splines, only: Coeffs, Eval > type, extends(coeffs) :: Coeffs_Q > contains > procedure :: Eval_Q > generic :: Eval =3D> Eval_Q > end type Coeffs_Q > integer, public, parameter :: QK =3D selected_real_kind ( 1 + precisio= n(1.0d0) ) > procedure :: Eval_Q =3D> Eval ( qk ) > end module Splines_Q >=20 > use Splines_Q, only: Coeffs_Q, DK, SK, QK > type(coeffs_q(dk)) :: C_D > type(coeffs_q(sk)) :: C_S > type(coeffs_q(qk)) :: C_Q > real(dk) :: Y_d > real(sk) :: Y_S > real(qk) :: Y_q > call c_d%eval ( 1.5_dk, y_d ) > call c_s%eval ( 1.5_sk, y_s ) > call c_q%eval ( 1.5_qk, y_q ) >=20 > Now let's do it using a parameterized module: >=20 > module Splines ( RK ) > integer, public, kind :: RK ! Module parameter > type :: Coeffs ! Doesn't have a type parameter > real(rk), allocatable :: A(:), B(:), C(:), D(:) > contains > procedure Eval > end type Coeffs > contains > subroutine Eval ( C, X, Y ) > class(coeffs), intent(in) :: C > real(rk), intent(in) :: X > real(rk), intent(out) :: Y > ... (don't need Include "Eval_Body.f9h") > end subroutine Eval > end module Splines >=20 > Now I need single, double and Q-precision splines: >=20 > use Splines ( kind(1.0d0) ), only: Coeffs_D =3D> Coeffs, DK =3D> RK > use Splines ( kind(1.0e0) ), only: Coeffs_S =3D> Coeffs, SK =3D> RK > use Splines ( selected_real_kind ( 1 + precision(1.0d0) ), only: Coeffs_= Q =3D> Coeffs, & > & QK =3D> RK >=20 > type(coeffs_d) :: C_D > type(coeffs_s) :: C_S > type(coeffs_q) :: C_Q > real(dk) :: Y_d > real(sk) :: Y_s > real(qk) :: Y_q > call c_d%eval ( 1.5_dk, y_d ) > call c_s%eval ( 1.5_rk, y_s ) > call c_q%eval ( 1.5_qk, y_q ) >=20 > This works, even if you don't have source code for the module. It's > easy to construct a type and consistent related type-bound procedures. > You can't do that nearly so easily using parameterized procedures > without parameterized modules. If you have a parameterized EVAL > procedure but you don't have the source for the Splines module, you need > to extend the type to add a binding for the Q-precision Eval subroutine. > It's not impossible, but it's ugly and requires more labor expense for > development and maintenance. >=20 > To make things a little bit smoother, we should allow declarations > before USE statements, so long as they depend only upon things declared > earlier (an already-ubiquitous requirement in the Fortran standard): >=20 > integer, parameter :: DK =3D kind(0.0d0) > integer, parameter :: SK =3D kind(0.0e0) > integer, parameter :: QK =3D selected_real_kind ( 1 + precision(1.0d0) ) >=20 > use Splines ( dk ), only: Coeffs_D =3D> Coeffs > use Splines ( sk ), only: Coeffs_S =3D> Coeffs > use Splines ( qk ), only: Coeffs_Q =3D> Coeffs >=20 > This was all laid out in much greater detail in 04-383r1, with many more > use case examples. >=20 >=20 > _______________________________________________ > J3 mailing list > J3@mailman.j3-fortran.org > http://mailman.j3-fortran.org/mailman/listinfo/j3 Bill Long = longb@cray.com Principal Engineer, Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9143 Cray Inc./ 2131 Lindau Lane/ Suite 1000/ Bloomington, MN 55425