Derived Type Procedures

Type-Bound Update

Mutating Self

A type-bound procedure can update the object when the passed object has intent(inout).

Program

Play the program to choose a delta and update a counter through a bound procedure.

type_bound_update.f90 
module counter_model
    implicit none
    type :: counter
        integer :: value
    contains
        procedure :: add
    end type counter
contains
    subroutine add(self, delta)
        class(counter), intent(inout) :: self
        integer, intent(in) :: delta
        self%value = self%value + delta
    end subroutine add
end module counter_model

program type_bound_update_demo
    use counter_model
    implicit none
    type(counter) :: hits
    integer :: delta

    hits = counter(10)
    delta = 
    call hits%add(delta)
    print '(I0)', hits%value
end program type_bound_update_demo

module counter_model
    implicit none
    type :: counter
        integer :: value
    contains
        procedure :: add
    end type counter
contains
    subroutine add(self, delta)
        class(counter), intent(inout) :: self
        integer, intent(in) :: delta
        self%value = self%value + delta
    end subroutine add
end module counter_model

program type_bound_update_demo
    use counter_model
    implicit none
    type(counter) :: hits
    integer :: delta

    hits = counter(10)
    delta = 
    call hits%add(delta)
    print '(I0)', hits%value
end program type_bound_update_demo

module counter_model
    implicit none
    type :: counter
        integer :: value
    contains
        procedure :: add
    end type counter
contains
    subroutine add(self, delta)
        class(counter), intent(inout) :: self
        integer, intent(in) :: delta
        self%value = self%value + delta
    end subroutine add
end module counter_model

program type_bound_update_demo
    use counter_model
    implicit none
    type(counter) :: hits
    integer :: delta

    hits = counter(10)
    delta = 
    call hits%add(delta)
    print '(I0)', hits%value
end program type_bound_update_demo
intent(inout) `intent(inout)` lets a procedure read and update the object.
subroutine method `call hits%add(delta)` invokes a mutating type-bound subroutine.
component update `self%value` names a component of the current object.