Fortran 2008 中类型绑定子例程中的可选参数

Question

调用类型绑定子例程的最佳方法是什么 seed_rng？

以下代码的编译命令gfortran -Wall mwe.f90产生警告

         subroutine seed_rng_sub ( self, checkOS, mySeed )
                                      1
Warning: Unused dummy argument ‘self’ at (1) [-Wunused-dummy-argument]

对于初学者来说，这建议删除子例程定义中的 self 参数（即使用 subroutine seed_rng_sub ( checkOS, mySeed )）。然而，这会产生错误

             procedure, public :: seed_rng => seed_rng_sub
                     1
Error: Non-polymorphic passed-object dummy argument of ‘seed_rng_sub’ at (1)

和

             class ( randomNumber ), target :: self
                                                  1
Error: CLASS variable ‘self’ at (1) must be dummy, allocatable or pointer

除了 Whosebug "Questions that may already have your answer"，我们还阅读了 http://comments.gmane.org/gmane.comp.gcc.fortran/33604 and https://gcc.gnu.org/ml/fortran/2010-09/msg00221.html 上的讨论，但没有成功。

主程序：

include 'mod test.f90'

program mwe

use mTest
implicit none

type ( randomNumber ) :: rnumber

    call rnumber % seed_rng ( .true. )

end program mew

模块：

module mTest

use iso_fortran_env, only: int64, real64

implicit none

type, public :: randomNumber

    real ( kind ( real64 ) ) :: x

    contains

        private

        ! subroutines
        procedure, public :: seed_rng => seed_rng_sub

end type randomNumber

private :: seed_rng_sub

contains

    subroutine seed_rng_sub ( self, checkOS, mySeed )

        use iso_fortran_env, only: int64

        class ( randomNumber ), target :: self

        integer, intent ( IN ), optional :: mySeed ( 1 : 12 )
        logical, intent ( IN ), optional :: checkOS

        integer :: n = 0
        integer, allocatable :: seed ( : )
        integer, parameter :: s0 ( 1 : 12 )  = [ 155719726,  156199294,  156319186,  156439078,  156678862,  156918646, &
                                                 157198394,  157318286,  157398214,  157438178,  157518106,  157877782  ]

            call random_seed ( size = n )
            allocate ( seed ( n ) )

            if ( present ( mySeed ) ) then
                call random_seed ( put = mySeed )
                return
            end if

            present_checkOS: if ( present ( checkOS ) ) then
                if ( checkOS ) then
                    call random_seed ( put = s0 )
                    return
                else
                    exit present_checkOS
                end if
            end if present_checkOS

            call random_seed ( put = s0 )

    end subroutine seed_rng_sub

end module mTest

Answer 1

据我所知，调用此函数有两种选择——使用或传递对象虚拟参数。

在您的版本中，

... 
procedure, public :: seed_rng => seed_rng_sub
...
subroutine seed_rng_sub ( self, checkOS, mySeed )
...
  class ( randomNumber ), target :: self
...

您将收到未使用 self 时看到的警告。如果你想避免警告，你可以不传递传递的对象，更改上面的前两行并删除第三行：

...
procedure, nopass, public :: seed_rng => seed_rng_sub
...
subroutine seed_rng_sub (checkOS, mySeed )
...

过程的 nopass 属性告诉 Fortran 不要传递传递对象伪参数，因此您可以从子例程声明中删除它并从该子例程中删除变量。当您尝试更改子例程时出现错误的原因是没有 nopass 属性，您仍在指定过程第一个参数是传递的对象伪参数并且您的过程不匹配。见分类。 4.5.4.5 Fortran 2008 进一步阅读。

Fortran 2008 中类型绑定子例程中的可选参数

Optional arguments in type bound subroutines in Fortran 2008

fortran

types

class

gfortran

polymorphic-associations