I just learned from Why are ref's in structs type unstable? that Ref is not a concrete type, and so structs containing a Ref are not type-stable, e.g. struct Foo a::Ref end Instead you have to use, for example, RefValue like struct Bar a::RefValue end As a new-ish user, who was introduced to…

I made an issue for this a bit ago too Ref docstring should note clearly that it's an abstract type · Issue #55321 · JuliaLang/julia · GitHub . I don’t really understand some of the responses made in that issue but hopefully this can be addressed at some point. Maybe commenting your support for the m…

[image] johnomotani: I’ve fallen into a pattern where when I want a mostly immutable struct, but one or two fields need to be mutable structs may have mutable struct fields.

@nsajko are you saying that I should replace struct Bar a::RefValue{Int64} end with mutable struct BazSubStruct b::Int64 end struct Baz a::BazSubStruct end ? That seems like quite a bit of boiler-plate code, which I’d only bother with if it was performance critical…

The other option that is available as of Julia 1.10 (iirc might be 1.9) is to make a mutable struct with const fields.

I just really don’t get why we can’t just at least export RefValue. The reasoning, and preference for requiring users to define whole new structs is just bizarre and user-hostile to me.

[image] johnomotani: That seems like quite a bit of boiler-plate code, which I’d only bother with if it was performance critical… Personally I don’t see that as an issue at all. Another alternative is to use a zero-dimensional array, e.g., Array{Int,0}. NB: mutable state is often a bad choic…

Zero dimensional arrays are worse, slower, and heavier than RefValues.

They’re supported, though. If this is such an issue, why not implement a zero dimensional array type as a simple mutable wrapper: mutable struct A{T} <: AbstractArray{T, 0} value::T end Base.getindex(a::A) = a.value ... Then put it in a package and register it.

I don’t think someone should have to make such a package when a perfectly fine RefValue exists, other than it not being public for whatever reason. People already use Ref for this (and not necessarily knowing about RefValue due to poor documentation).

[image] DanielVandH: a perfectly fine RefValue exists, other than it not being public for whatever reason If you don’t know the reason for it not being public, why are you advocating making it public? Or maybe just make a PR making it public and see what the devs will say.

I’ve already made the thread linked in my first reply? By “for whatever reason” maybe replace it with a bizarre reason - see the linked thread.

Ref is not a concrete type - poorly documented?

General Usage Performance

nsajko April 12, 2025, 10:18am 18

Done:

Topic		Replies	Views
Why are ref's in structs type unstable? Performance type-stability	4	635	April 26, 2022
Ref{T} vs Base.RefValue{T} Performance	20	601	April 10, 2025
Type instabilities when dealing with structs and Ref Performance struct , code_warntype , type-stability	4	322	June 3, 2024
Type instability of reference struct member General Usage	3	150	June 22, 2025
Question on RefValue General Usage	12	2818	January 18, 2021

Ref is not a concrete type - poorly documented?

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