Constrained genericity: Difference between revisions

=={{header|Fortran}}==

In Fortran all checkes are done at compile time, in particular a dummy argument has to conform class.

<lang fortran>

module cg

implicit none

type, abstract :: eatable

end type eatable

type, extends(eatable) :: carrot_t

end type carrot_t

type :: brick_t; end type brick_t

type :: foodbox

class(eatable), allocatable :: food

contains

procedure, public :: add_item => add_item_fb

end type foodbox

contains

subroutine add_item_fb(this, f)

class(foodbox), intent(inout) :: this

class(eatable), intent(in) :: f

allocate(this%food, source=f)

end subroutine add_item_fb

end module cg

program con_gen

use cg

implicit none

type(carrot_t) :: carrot

type(brick_t) :: brick

type(foodbox) :: fbox

! Put a carrot into the foodbox

call fbox%add_item(carrot)

! Try to put a brick in - results in a compiler error

call fbox%add_item(brick)

end program con_gen

</lang>

{{out}}

ifort -o cg cg.f90

<pre>

cg.f90(40): error #6633: The type of the actual argument differs from the type of the dummy argument. [BRICK]

call fbox%add_item(brick)

</pre>

gfortran -o cg cg.f90

<pre>

cg.f90:41.23:

call fbox%add_item(brick)

1

Error: Type mismatch in argument 'f' at (1); passed TYPE(brick_t) to CLASS(eatable)

</pre>