2016 Update

Task/Constrained-genericity/Fortran/constrained-genericity.f

@@ -0,0 +1,42 @@
+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