# Is this generated function for struct2tuple safe to use?
**URL:** https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086
**Category:** General Usage
**Tags:** runtimegeneratedfunc, generated
**Created:** [September 4, 2025, 1:42am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086 "2025-09-04T01:42:36Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Tortar](https://discourse.julialang.org/u/Tortar)
#### Post date: [September 4, 2025, 1:42am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/1 "2025-09-04T01:42:36Z")
I’m not really sure if this function could be used safely when I have a struct with mutable fields in it:
```julia-auto
@generated function struct2tuple(x::T) where T
n = fieldcount(T)
exprs = [:(getfield(x, $(i))) for i in 1:n]
return Expr(:tuple, exprs...)
end
```
is it forbidden? It seems that the manual says something against this when talking about observing mutable states, but it seems to work fine e.g.
```julia-auto
julia> struct A
x::Vector{Int}
y::Vector{Float64}
end
julia> struct2tuple(A([1], [1.]))
([1], [1.0])
```
But I’m a total beginner in these kind of things so I’m unsure.
---
### Author:  [@Tortar](https://discourse.julialang.org/u/Tortar)
#### Post date: [September 4, 2025, 2:11am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/2 "2025-09-04T02:11:07Z")
Maybe I’m wrong, but if “observing mutable states” means that I base any code generation decision on mutable values, then this should be safe.
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [September 4, 2025, 2:34am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/3 "2025-09-04T02:34:45Z")
> Generated functions must not _mutate_ or _observe_ any non-constant global state (including, for example, IO, locks, non-local dictionaries, or using [`hasmethod`](https://docs.julialang.org/en/v1/base/base/#Base.hasmethod)).
you’re fine I think, you’re not mutating any non-constant global state, and I don’t think `fieldcount(T)` is a mutable global state.
---
### Author:  [@oxinabox](https://discourse.julialang.org/u/oxinabox)
#### Post date: [September 4, 2025, 4:08am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/4 "2025-09-04T04:08:43Z")
technically `fieldcount` is a generic function which could be overloaded for a specific type.
But if that happens a lot of other things will probably break,
so you are already in hell.
This code is fine basically.
---
### Author:  [@matthias314](https://discourse.julialang.org/u/matthias314)
#### Post date: [September 4, 2025, 5:42am UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/5 "2025-09-04T05:42:04Z")
This doesn’t answer your question, but in your specific case you can replace the generated function by
```julia-auto
struct2tuple(x::T) where T = ntuple(i -> getfield(x, i), Val(fieldcount(T)))
```
(I didn’t check that this remains efficient for structs with very many fields.)
---
### Author:  [@Tortar](https://discourse.julialang.org/u/Tortar)
#### Post date: [September 4, 2025, 1:22pm UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/6 "2025-09-04T13:22:53Z")
Nice, yes, it seems to work fine in my use case. I had the same function without the `Val` and it wasn’t working efficiently, but with that it does.
Thanks a lot to all of you!
---
### Author:  [@aplavin](https://discourse.julialang.org/u/aplavin)
#### Post date: [September 4, 2025, 10:42pm UTC](https://discourse.julialang.org/t/is-this-generated-function-for-struct2tuple-safe-to-use/132086/7 "2025-09-04T22:42:56Z")
Also check ConstructionBase.jl: it has `getfields(your_obj)` and `getproperties(your_obj)`.
It’s a very lightweight package, a large fraction of Julia ecosystem depends on it.