Object-Oriented Programming (OOP)

This example shows how to define and use derived types with inheritance and type-bound procedures.

fortranCopy codemodule shapes
    implicit none

    type :: shape
        contains
        procedure :: area => shape_area
    end type shape

    type, extends(shape) :: circle
        real :: radius
    contains
        procedure :: area => circle_area
    end type circle

    type, extends(shape) :: rectangle
        real :: length, width
    contains
        procedure :: area => rectangle_area
    end type rectangle

contains

    function shape_area(this) result(area)
        class(shape), intent(in) :: this
        real :: area
        area = 0.0
    end function shape_area

    function circle_area(this) result(area)
        class(circle), intent(in) :: this
        real :: area
        area = 3.14159 * this%radius**2
    end function circle_area

    function rectangle_area(this) result(area)
        class(rectangle), intent(in) :: this
        real :: area
        area = this%length * this%width
    end function rectangle_area

end module shapes

program test_oop
    use shapes
    implicit none

    type(circle) :: my_circle
    type(rectangle) :: my_rectangle

    my_circle%radius = 5.0
    my_rectangle%length = 4.0
    my_rectangle%width = 6.0

    print *, 'Circle area: ', my_circle%area()
    print *, 'Rectangle area: ', my_rectangle%area()
end program test_oop