# Struct with optional self type member crashes
**URL:** https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336
**Category:** Mojo
**Created:** [April 29, 2025, 3:11pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336 "2025-04-29T15:11:49Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@ratulb](https://forum.modular.com/u/ratulb)
#### Post date: [April 29, 2025, 3:11pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/1 "2025-04-29T15:11:49Z")
I have the following mojo code - it just crashes!
```mojo
fn main():
_e = Employee("me", None)
@value
struct Employee:
var name: String
var assistant: Optional[Employee]
```
How can I achieve what I am looking for?
**mojo version: mojo 25.3.0.dev2025042905 (b3907eb3)**
---
### Author:  [@owenhilyard](https://forum.modular.com/u/owenhilyard)
#### Post date: [April 29, 2025, 3:51pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/2 "2025-04-29T15:51:24Z")
Please file a bug. This should be a compiler error instead of a crash.
The reason you can’t do this is because the type has infinite size. Unlike in Python, `Optional[Employee]` is a single allocation, which contains an `Optional[Employee]`, and so on.
This would work for you:
```auto
from memory import OwnedPointer
fn main():
_e = Employee("me", None)
@value
struct Employee:
var name: String
var assistant: Optional[OwnedPointer[Employee]]
```
But right now we’re reworking parts of the standard library so there’s an interface conflict.
---
### Author:  [@sora](https://forum.modular.com/u/sora)
#### Post date: [April 29, 2025, 4:41pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/3 "2025-04-29T16:41:18Z")
Have you tried this code? `OwnedPointer` doesn’t type check, and `ArcPointer` seg faults. 🙃
---
### Author:  [@owenhilyard](https://forum.modular.com/u/owenhilyard)
#### Post date: [April 29, 2025, 4:42pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/4 "2025-04-29T16:42:43Z")
See my last sentence.
---
### Author:  [@ratulb](https://forum.modular.com/u/ratulb)
#### Post date: [April 29, 2025, 4:52pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/5 "2025-04-29T16:52:00Z")
That did not work. Below are the errors that I get:
```mojo
error: cannot bind type 'OwnedPointer[Employee]' to trait 'Copyable & Movable'
var assistant: Optional[OwnedPointer[Employee]]
~~~~~~~~~~~~^~~~~~~~~~
note: struct 'OwnedPointer[T]' does not implement all requirements for 'Copyable'
note: required function ' __copyinit__' is not implemented
```
---
### Author:  [@owenhilyard](https://forum.modular.com/u/owenhilyard)
#### Post date: [April 29, 2025, 4:53pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/6 "2025-04-29T16:53:31Z")
> But right now we’re reworking parts of the standard library so there’s an interface conflict.
What I was trying to say with this is that there isn’t a good way to do this at the moment in safe Mojo. We’re in the middle of applying some recent advancements to the type system.
---
### Author:  [@miktavarez](https://forum.modular.com/u/miktavarez)
#### Post date: [April 29, 2025, 5:12pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/7 "2025-04-29T17:12:33Z")
It’s not great at the moment. I opted to use a list of arcpointers for my project: [prism/src/prism/command.mojo at main · thatstoasty/prism · GitHub](https://github.com/thatstoasty/prism/blob/main/src/prism/command.mojo#L116)
Previously it was an `ArcPointer[Optional[Self]]` which worked, but `Optional[ArcPointer[Self]]` did not 🙂
---
### Author:  [@system](https://forum.modular.com/u/system)
#### Post date: [October 26, 2025, 5:13pm UTC](https://forum.modular.com/t/struct-with-optional-self-type-member-crashes/1336/8 "2025-10-26T17:13:13Z")
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.