Add notes from talking through

Author: znicholls

NOTES.md

@@ -0,0 +1 @@
+- TODO: ZN to write implementation notes and why we don't use a pure pointer based solution

src/example_fgen_basic/error_v/creation.f90

@@ -36,7 +36,7 @@ function create_error(inv) result(err)
         if (mod(inv, 2) .eq. 0) then
             err = ErrorV(code=1, message="Even number supplied")
         else
-            err = ErrorV(code=0)
+            err = ErrorV(code=NO_ERROR_CODE)
         end if
 
     end function create_error

src/example_fgen_basic/error_v/creation_wrapper.f90

@@ -39,15 +39,15 @@ subroutine create_error(inv, res_instance_index)
 
         type(ErrorV), pointer :: res
 
+        ! Use the pointer more or less like a normal instance of the derived type
+        res = o_create_error(inv)
+
         ! This is the other trick for wrapping.
         ! We have to ensure that we have correctly associated pointers
         ! with the derived type instances we want to 'pass' across the Python-Fortran interface.
         ! Once we've done this, we can then set them more or less like normal derived types.
         res_instance_index = error_v_manager_get_free_instance_number()
         call error_v_manager_associate_pointer_with_instance(res_instance_index, res)
-
-        ! Use the pointer more or less like a normal instance of the derived type
-        res = o_create_error(inv)
         ! Ensure that the instance index is set correctly
         res % instance_index = res_instance_index
 

src/example_fgen_basic/error_v/error_v.f90

@@ -33,6 +33,7 @@ module m_error_v
         ! (means you can stop but also unwind errors and traceback along the way)
 
         ! TODO: think about adding trace (might be simpler than compiling with traceback)
+        ! type(ErrorV), allocatable, dimension(:) :: causes
 
     contains
 

src/example_fgen_basic/error_v/error_v_manager.f90

@@ -44,6 +44,7 @@ function get_free_instance_number() result(instance_index)
 
     end function get_free_instance_number
 
+    ! Might be a better way to do this as the pointers are a bit confusing, let's see
     subroutine associate_pointer_with_instance(instance_index, instance_pointer)
         !! Associate a pointer with the instance corresponding to the given model index
         !!

src/example_fgen_basic/error_v/error_v_wrapper.f90

@@ -48,6 +48,7 @@ subroutine iget_message( &
 
         integer, intent(in) :: instance_index
 
+        ! TODO: make this variable length
         character(len=128), intent(out) :: message
 
         type(ErrorV), pointer :: instance

src/example_fgen_basic/fpyfgen/derived_type_manager_helpers.f90

@@ -51,6 +51,8 @@ subroutine get_derived_type_free_instance_number(instance_index, n_instances, in
 
         end do
 
+        ! Should be an error or similar here
+
     end subroutine get_derived_type_free_instance_number
 
     subroutine finalise_derived_type_instance_number(instance_index, n_instances, instance_avail, instance_array)