如何在 Fortran 类中将子例程名称作为参数传递

Question

在How to pass subroutine names as arguments in Fortran? 中，我们学习了如何在 Fortran 中将子例程名称作为参数传递。我们如何在类结构中做到这一点？

随后的代码使用 GNU Fortran (GCC) 5.1.0 产生以下编译错误：

gfortran  -Wall -Wextra -Wconversion -Og -pedantic -fcheck=bounds -fmax-errors=5 class_pass.f08 
myClass.f08:44:30:

                 class ( test ), target :: me
                              1
Error: Derived type ‘test’ at (1) is being used before it is defined
myClass.f08:9:21:

             procedure, public :: action => action_sub
                     1
Error: Non-polymorphic passed-object dummy argument of ‘action_sub’ at (1)
myClass.f08:40:36:

         class ( test ), target :: me
                                    1
Error: CLASS variable ‘me’ at (1) must be dummy, allocatable or pointer
(null):0: confused by earlier errors, bailing out

主要程序如下。它包括一个用作诊断的例程check。

include 'myClass.f08'
program class_pass

    use myClass
    implicit none

    type ( test ) :: myTest

        call myTest % check ()
        call myTest % action ( square_sub )

end program class_pass

模块：

module myClass

    implicit none

    type     :: test
        real :: x, y
        contains
            private
            procedure, public :: action => action_sub
            procedure, public :: square => square_sub
            procedure, public :: double => double_sub
            procedure, public :: check  => check_sub
    end type test

    private :: action_sub
    private :: square_sub
    private :: double_sub
    private :: check_sub

contains

    subroutine square_sub ( me )
        class ( test ), target :: me
            me % y = me % x ** 2
    end subroutine square_sub

    subroutine double_sub ( me )
        class ( test ), target :: me
            me % y = me % x * 2
    end subroutine double_sub

    subroutine check_sub ( me )
        class ( test ), target :: me
            me % x = 5.0
            call double_sub ( me )
            print *, 'x = ', me % x, ', y = ', me % y
    end subroutine check_sub

    subroutine action_sub ( sub )
        class ( test ), target :: me

        interface mySub
            subroutine sub ( me )
                class ( test ), target :: me
            end subroutine sub
        end interface mySub

            call sub ( me )
            print *, 'x = ', me % x, ', y = ', me % y

    end subroutine action_sub

end module myClass

非常感谢 @Vladimir F 提供的原始解决方案和提示。

Answer 1

您的错误是由于您的程序action_sub 中缺少参数以及其他一些小问题。此过程通过

绑定到您的派生类型

procedure, public :: action => action_sub

默认情况下，多态类变量作为第一个参数传递给action_sub。您已在其他类型绑定的过程中正确地考虑了这一点，但在此过程中缺少它。您还需要在action_sub 的接口块中导入派生类型，以便在那里使用该类型。这个过程的修改版本允许您的模块正确编译：

subroutine action_sub ( me, sub )
    class ( test ), target :: me

    interface mySub
        subroutine sub ( me )
            import test
            class ( test ), target :: me
        end subroutine sub
    end interface mySub

        call sub ( me )
        print *, 'x = ', me % x, ', y = ', me % y

end subroutine action_sub

接下来，在你做的主程序中：

call myTest % action ( square_sub )

为了在此处引用square_sub，您需要在您的模块中公开该过程。从模块过程中删除 private 属性后，您的代码将编译并运行：

 x =    5.00000000     , y =    10.0000000
 x =    5.00000000     , y =    25.0000000