Fortran 状态模式

为了增强计算机程序的健壮性，关于Fortran的设计模式网上资料难以查找，于是借鉴go语言的状态模式，改编出了Fortran的状态模式。

module context
    implicit none

    type, public :: HungryState
        logical :: State
    contains
        procedure :: HungryProcedure
        procedure :: NoHungryProcedure
    end type

    type, public :: Person
        type(HungryState) :: HungryState
    contains
        procedure :: Eat
        procedure :: Work
    end type

    type, public :: Hungry
    end type

    type, public :: NoHungry
    end type

contains

    subroutine Eat(this)
        class(Person)  :: this
        if (this % HungryState % state) then
            write(6, "(A)") "Eatting.."
            !!// 改变状态
            call this % HungryState % NoHungryProcedure
        else
            write(6, "(A)") "Already baole!!"
        end if
    end subroutine

    subroutine Work(this)
        class(Person) :: this
        if (this % HungryState % state) then
            write(6, "(A)") "I am hungry, no work!!"
        else
            write(6, "(A)") "Ok, let us do work.."
            call this % HungryState % HungryProcedure
        end if
    end subroutine

    subroutine HungryProcedure(this)
        class(HungryState) :: this
        this % state = .true.
    end subroutine

    subroutine NoHungryProcedure(this)
        class(HungryState) :: this
        this % state = .false.
    end subroutine

end module

program main
    use context
    implicit none
    type(Person) :: p
    call p % HungryState % NoHungryProcedure
    call p % Eat
    call p % Work
    call p % Eat
    call p % Eat
end program