# Pointer vs Allocatable With Arjen **URL:** \ **Category:** Tutorials\ **Created:** [October 2, 2020, 1:51pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325 "2020-10-02T13:51:29Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [October 2, 2020, 1:51pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/1 "2020-10-02T13:51:30Z")
Arjen and I had a discussion about pointer and allocatable variables. You can watch our talk on YouTube. [![](https://global.discourse-cdn.com/free1/uploads/fortran_lang/original/1X/0a6c143adf8546779b3576ad2dc7a1f210e51bba.jpeg "Fortran Pointer Vs Allocatable With Arjen Markus") ](https://www.youtube.com/watch?v=hPBGpyX--W8) ---
**Author:** ![milancurcic](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/milancurcic/32/2_2.png) [@milancurcic](https://fortran-lang.discourse.group/u/milancurcic)\ **Post date:** [October 2, 2020, 7:54pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/2 "2020-10-02T19:54:57Z")
I enjoyed this conversational format very much, do more of that. ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [October 2, 2020, 8:04pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/3 "2020-10-02T20:04:05Z")
I’m glad you liked it. I’ve already got an idea for a follow up, so I’ll keep going so long as I can keep getting volunteers (hint hint to anybody interested in contributing). ---
**Author:** ![certik](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/certik/32/4_2.png) [@certik](https://fortran-lang.discourse.group/u/certik)\ **Post date:** [October 2, 2020, 8:25pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/4 "2020-10-02T20:25:30Z")
I like this. The other thing you can do is interviews with members of the community and have a channel at youtube (or elsewhere). I think this can greatly help getting to know each other better. ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [October 2, 2020, 8:37pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/5 "2020-10-02T20:37:08Z")
I like the idea. Maybe if you get the J3 Chair position you might volunteer for the first one? 😉 ---
**Author:** ![certik](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/certik/32/4_2.png) [@certik](https://fortran-lang.discourse.group/u/certik)\ **Post date:** [October 2, 2020, 9:36pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/6 "2020-10-02T21:36:59Z")
I’ll be happy to. 🙂 ---
**Author:** ![lkedward](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/lkedward/32/72_2.png) [@lkedward](https://fortran-lang.discourse.group/u/lkedward)\ **Post date:** [October 3, 2020, 5:21pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/7 "2020-10-03T17:21:18Z")
Interesting and insightful conversation! Thanks for sharing. Regarding the deallocation of pointers in finalisers, the problem raised in your conversation is solved by reference counting in defined assignment; this allows you to return such objects from functions without having the pointer deallocated since the assignment necessarily occurs before the function result finaliser is called. ---
**Author:** ![jeremie.vandenplas](https://avatars.discourse-cdn.com/v4/letter/j/76d3ee/32.png) [@jeremie.vandenplas](https://fortran-lang.discourse.group/u/jeremie.vandenplas)\ **Post date:** [October 3, 2020, 6:14pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/8 "2020-10-03T18:14:54Z")
I like this format and the conversation. Thank you for sharing it. ---
**Author:** ![nshaffer](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/nshaffer/32/161_2.png) [@nshaffer](https://fortran-lang.discourse.group/u/nshaffer)\ **Post date:** [October 5, 2020, 2:14pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/9 "2020-10-05T14:14:13Z")
Nice! I came into it expecting something with more structure rather than a softly guided conversation, but once I adjusted that expectation, I quite liked it. Thanks Arjen and Brad! In the code that I’ve read, the most common use of pointers has been to give a name to an array section to make it convenient to assign to or use in expressions, e.g., ```auto implicit none real, target :: r(3, 5) real, pointer :: x(:), y(:), z(:) integer :: i x => r(1,:) y => r(2,:) z => r(3,:) x = [(1.0*i, i=1,size(x))] y = [(10.0*i, i=1,size(y))] z = [(100.0*i, i=1,size(z))] print *, r ! 1.0 10.0 100.0 2.0 20.0 200.0 ... nullify (x, y, z) end ``` But I suspect that kind of usage happens when one doesn’t know about `associate` ```auto implicit none real :: r(3, 5) integer :: i associate (x => r(1,:), y => r(2,:), z => r(3,:)) x = [(1.0*i, i=1,size(x))] y = [(10.0*i, i=1,size(y))] z = [(100.0*i, i=1,size(z))] end associate print *, r ! 1.0 10.0 100.0 2.0 20.0 200.0 ... end ``` Of course, the pointer version lets `x`, `y`, and `z` cross procedure boundaries, but the chat did a nice job of highlighting that this can introduce subtle bugs, especially if the target array is an allocatable. ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [October 5, 2020, 5:11pm UTC](https://fortran-lang.discourse.group/t/pointer-vs-allocatable-with-arjen/325/10 "2020-10-05T17:11:02Z")
I’m glad you liked it. I’m actually planning to record a discussion with Damian Rouson about this exact approach, as he recently sent me a paper he wrote a while back doing just that. [This Isn’t Your Parents’ Fortran: Managing C++ Objects with Modern Fortran](https://www.computer.org/csdl/magazine/cs/2012/02/mcs2012020046/13rRUxCitDc)