Environment
Visual Studio 2022 : 17.14.21
IFX : 2025.3.0
Problem
In debug mode, Visual Studio cannot display correct Watch values for a polymorphic (class) allocatable array.
type :: Layer
!...
end type Layer
type extends(Layer):: extended_Layer
!...
end type extended_Layer
class(layer),allocatable,dimension(:):: L
allocate(extended_Layer::L(5))situation 1
Right after allocation, I cannot inspect L correctly in the Watch window.
situation 2
Even if I use select type, I still can’t inspect the variable properly inside the type is block:
select type (L)
type is (extended_Layer)
! ...
end selectThe Watch window shows an incorrect upper bound for L (e.g., -1) as below, although print statements show the correct values at runtime.
Does this mean IFX + Visual Studio currently cannot reliably display polymorphic (class) variables in Watch?
If so, is the recommended workaround to use print statements, or to pass the object into a subroutine with a non-polymorphic dummy argument?
Thanks in advance.
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Thanks for your reply, and I'm sorry for the late follow-up.
I'll share a simple program below-just copy/paste it into an empty Fortran project and it should run.
module simple_class
implicit none(external)
private
public :: basic_layer, advanced_layer,alayer_1
type basic_layer
integer :: layer_id
double precision:: dx,dy
end type basic_layer
type ,extends(basic_layer) :: advanced_layer
double precision :: dz
end type advanced_layer
class(basic_layer),allocatable :: alayer_1(:)
contains
end module simple_class
program main
use simple_class,only: advanced_layer,basic_layer,alayer_1
type(basic_layer) :: layer1
type(advanced_layer) :: layer2
class(basic_layer),allocatable :: layer3,layer4
!===successful watcher debug session===
layer1%layer_id = 1
layer1%dx = 0.1d0;layer1%dy = 0.2d0
continue
layer2%layer_id = 2
layer2%dx = 0.3d0;layer2%dy = 0.4d0;layer2%dz = 0.5d0
continue
allocate(basic_layer::layer3)
select type(layer3) ! to confirm the dynamic type
type is (basic_layer)
layer3%layer_id = 3
layer3%dx = 0.6d0;layer3%dy = 0.7d0
end select
continue
allocate(advanced_layer::layer4)
select type(layer4) ! to confirm the dynamic type
type is(advanced_layer)
layer4%layer_id = 4
layer4%dx = 0.8d0;layer4%dy = 0.9d0;layer4%dz = 1.0d0
print *, "layer4%dz =", layer4%dz
end select
continue
!===successful watcher debug session===
!===failure watcher debug session===
allocate(advanced_layer::alayer_1(3))
select type(alayer_1) ! to confirm the dynamic type
type is(advanced_layer)
alayer_1(:)%layer_id = 5
alayer_1(:)%dx = 1.1d0;alayer_1(:)%dy = 1.2d0;alayer_1(:)%dz = 1.3d0
print *, "alayer_1(1)%dz =", alayer_1(1)%dz
end select
continue
!===failure watcher debug session===
!===successful watcher debug session===
!-use block to see the content
test : block
type(advanced_layer) :: aLayer(3)
select type(alayer_1) ! to confirm the dynamic type
type is (advanced_layer)
aLayer = alayer_1
end select
continue
end block test
!===successful watcher debug session===
end program mainAs shown in comments:
- If I define a variable as type(layer1,layer2) or as a scalar class (layer3,layer4), it can be inspected correctly in the debug Watch window.
- However, when I define an array of class, the Watch failed and shows stange values (like in the picture below).
For now, the only workaround I have is the last "block" part: by assigning an element into a specific type variable (aLayer),I can watch this aLayer variable to check the original variable. But it's tedious to insert this block everywhere just for debugging.
Is it simply hard(or unsupported) for the debugger to inspect an array of class objects? Even though the OOP part in fortran attract me a lot.
Thanks in advance!
I cannot see the variables and it crashes the debugger, your method will work it is not elegant, and in pure math not elegant is the kiss of death.
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