错误：如果 SELECT TYPE 中的选择器表达式不是命名变量，则应出现 Associate-name=>

Question

我正在尝试使用另一种类型的类型。但是，我不能让它编译。我很奇怪：选择类型的东西在主程序中工作，但它在类型的子例程中不起作用。

module ModBuffer
    implicit none
    private
    type, abstract, public :: Buffer
    contains
        procedure, public                       :: Constructor
    endtype Buffer

    type, extends(Buffer), public :: BufferR
        real(8), allocatable, public            :: BufData(:,:,:)
    endtype BufferR

    type, extends(Buffer), public :: BufferI
        complex(8), allocatable, public         :: BufData(:,:,:)
    endtype BufferI

    contains

    subroutine Constructor(this, dim1, dim2, dim3)
        class(Buffer), intent(inout)            :: this
        integer, intent(in)                     :: dim1, dim2, dim3

        select type(this)
        type is(BufferR)
            allocate(this%BufData(dim1, dim2, dim3))
        type is(BufferI)
            allocate(this%BufData(dim1, dim2, dim3))
        endselect
    endsubroutine Constructor
endmodule ModBuffer

module ModSystem
    use ModBuffer
    implicit none
    private
    type, public :: System
        class(Buffer), allocatable, public :: WF
    contains
    endtype System

    type, extends(System) :: NewSystem
    contains
        procedure, public :: Constructor
    endtype NewSystem

    contains

    subroutine Constructor(this, Flag)
        class(NewSystem), intent(inout) :: this
        logical, intent(in) :: Flag

        if(Flag) then
            allocate(BufferR::this%WF)
        else
            allocate(BufferI::this%WF)
        endif
        select type(this%WF)
        type is(BufferR)
            print *, "Buffer is real."
        type is(BufferI)
            print *, "Buffer is complex."
        endselect
    endsubroutine Constructor
endmodule ModSystem


program test
    use ModSystem
    !use Operation
    class(System), allocatable :: s

    allocate(NewSystem::s)
    call s%Constructor(.true.)
endprogram test

我得到了一个编译错误select type(this%WF)。但是如果我在主程序中定义一个 Buffer 类型并做同样的事情，就不会出错。

错误信息是：

error #8253: If selector expression in SELECT TYPE is not a named variable, associate-name=> shall appear.

我怎样才能编译这段代码？

Answer 1

没有理由用指针，只用关联部分select type（你没有写错误信息，但是IIRC它的描述性很强）：

   select type (twf => this%WF)