将常量命名为派生数据类型的组成部分 [英] Named constants as components of a derived data type

问题描述

似乎Fortran 90不允许在派生数据类型中使用命名常量.这是真的?以下代码不起作用.

It seems Fortran 90 does not allow named constants in derived data types. Is this true? The following code does not work.

program my_prog
implicit none
   type :: my_type
      integer, parameter :: a = 1
      real(kind(1.d0))   :: b
   end type my_type
   type (my_type) :: complex_type
end program my_prog

编译器说派生类型定义中不允许使用参数语句.

The compiler says parameter statement is not permitted in derived type definitions.

当我删除 parameter 关键字时，一切正常.但是，如何确定组件 a 在其他地方没有被修改?

When I remove the parameter keyword everything works fine. But then how can I make sure that the component a is not modified elsewhere?

推荐答案

根据标准，不允许使用.对于Fortran 90/95，组件属性说明符只能是 pointer 和 dimension (第4.4.1节)，此外， allocatable (在Fortran 2003中)(第4.5.3节)，以及 codimension 和 contiguous (对于Fortran 2008)(第4.5.4.1节).

According to the Standard, it is not allowed. The component attribute specifier may only be pointer, and dimension for Fortran 90/95 (section 4.4.1), additionally allocatable in Fortran 2003 (Section 4.5.3), and additionally codimension, and contiguousfor Fortran 2008 (section 4.5.4.1).

您可以在此处获取文档.

我在 target 说明符中遇到了类似的问题，这也是不允许的.

I ran into a similar problem with the target specifier, that is also not allowed.

为什么不尝试 private 组件?

module typedef
  type :: my_type
    integer, private :: a_int = 1
    real(kind(1.d0)) :: b
  contains
    procedure :: a
  end type my_type

contains
  function a(complex_type)
    class(my_type),intent(in) :: complex_type
    integer :: a
    a = complex_type%a_int
  end function
end module

program my_prog
  use typedef
  implicit none

  type (my_type) :: complex_type

  complex_type%b = 2.d0 ! This should work
  write(*,*) complex_type%a(), complex_type%b

!  complex_type%a_int = 3    ! This should fail

end program my_prog

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