备忘录模式

正文：https://refactoringguru.cn/design-patterns/memento

Go代码：https://refactoringguru.cn/design-patterns/memento/go/example

module memento_module

    implicit none
    private

    public :: caretaker_type, originator_type

    type originator_type
        character(:), allocatable :: state
    contains
        procedure :: create_memento => originator_t_create_memento
        procedure :: restore_memento => originator_t_restore_memento
        procedure :: set_state => originator_t_set_state
        procedure :: get_state => originator_t_get_state
    end type originator_type

    type memento_type
        character(:), allocatable :: state
    end type memento_type

    type caretaker_type
        type(memento_type), allocatable :: memento(:)
    contains
        procedure :: add_memento => caretaker_t_add_memento
        procedure :: get_memento => caretaker_t_get_memento
    end type caretaker_type

contains

    function originator_t_create_memento(self) result(memento)
        class(originator_type), intent(inout) :: self
        type(memento_type) :: memento
        memento%state = self%state
    end function originator_t_create_memento

    subroutine originator_t_restore_memento(self, memento)
        class(originator_type), intent(inout) :: self
        type(memento_type), intent(in) :: memento
        self%state = memento%state
    end subroutine originator_t_restore_memento

    subroutine originator_t_set_state(self, state)
        class(originator_type), intent(inout) :: self
        character(*), intent(in) :: state
        self%state = state
    end subroutine originator_t_set_state

    function originator_t_get_state(self) result(state)
        class(originator_type), intent(inout) :: self
        character(:), allocatable :: state
        state = self%state
    end function originator_t_get_state

    subroutine caretaker_t_add_memento(self, memento)
        class(caretaker_type), intent(inout) :: self
        type(memento_type), intent(in) :: memento
        self%memento = [self%memento, memento]
    end subroutine caretaker_t_add_memento

    function caretaker_t_get_memento(self, index) result(memento)
        class(caretaker_type), intent(inout) :: self
        integer, intent(in) :: index
        type(memento_type) :: memento
        memento = self%memento(index)
    end function caretaker_t_get_memento

end module memento_module

program memento_main

    use memento_module, only: caretaker_type, originator_type

    type(caretaker_type) :: caretaker
    type(originator_type) :: originator

    allocate (caretaker%memento(0))
    originator%state = "A"

    print *, "Originator state: ", originator%get_state()
    call caretaker%add_memento(originator%create_memento())

    call originator%set_state("B")
    print *, "Originator current state: ", originator%get_state()
    call caretaker%add_memento(originator%create_memento())

    call originator%set_state("C")
    print *, "Originator current state: ", originator%get_state()
    call caretaker%add_memento(originator%create_memento())

    call originator%restore_memento(caretaker%get_memento(2))
    print *, "Restored to state: ", originator%get_state()

    call originator%restore_memento(caretaker%get_memento(1))
    print *, "Restored to state: ", originator%get_state()

end program memento_main

!> Results shall be:

!  Originator state: A
!  Originator current state: B
!  Originator current state: C
!  Restored to state: B
!  Restored to state: A