# Segfault when using promote\_typejoin to control small union behaviour over parametric type

**URL:** <https://discourse.julialang.org/t/segfault-when-using-promote-typejoin-to-control-small-union-behaviour-over-parametric-type/23666>\
**Category:** General Usage\
**Tags:** parametric-types\
**Created:** [April 29, 2019, 7:54pm UTC](https://discourse.julialang.org/t/segfault-when-using-promote-typejoin-to-control-small-union-behaviour-over-parametric-type/23666 "2019-04-29T19:54:20Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![cstjean](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cstjean/32/1444_2.png) [@cstjean](https://discourse.julialang.org/u/cstjean)\
**Post date:** [April 29, 2019, 7:54pm UTC](https://discourse.julialang.org/t/segfault-when-using-promote-typejoin-to-control-small-union-behaviour-over-parametric-type/23666/1 "2019-04-29T19:54:20Z")

</div>

I have a parametric type `AtLeast{T}(x::T)`, and I’d like my broadcasts over vectors of `Union{Float64, AtLeast}` to propagate its type, instead of becoming `Any`. Following the discussion in [this post](https://discourse.julialang.org/t/small-union-type-failure/18640), I do this:

```julia
julia> struct AtLeast{T}
           x::T
       end

julia> a = [1.0, AtLeast(1.0)]
2-element Array{Any,1}:
 1.0                   
  AtLeast{Float64}(1.0)

julia> identity.(a) # bad
2-element Array{Any,1}:
 1.0                   
  AtLeast{Float64}(1.0)

julia> Base._promote_typejoin(::Type{A}, ::Type{T}) where {T, A<:AtLeast} =
           isconcretetype(T) || T === Union{} ? Union{T, A} : Any

julia> Base._promote_typejoin(::Type{T}, ::Type{A}) where {T, A<:AtLeast} =
           isconcretetype(T) || T === Union{} ? Union{T, A} : Any

julia> identity.(a) # good
2-element Array{Union{Float64, AtLeast{Float64}},1}:
 1.0                   
  AtLeast{Float64}(1.0)

```

All’s well, but when I put these two `_promote_typejoin` lines into my (large) module, precompilation segfaults on Julia 1.1, Linux. I’ve tried to bisect it to a MWE, but after one hour of toil, I just found out that it depends on another of our private modules, and Unitful (at least). Gah. Am I doing anything wrong?

```julia
signal (6): Aborted
in expression starting at no file:0
raise at /build/glibc-LK5gWL/glibc-2.23/signal/../sysdeps/unix/sysv/linux/raise.c:54
abort at /build/glibc-LK5gWL/glibc-2.23/stdlib/abort.c:89
jl_intref at /buildworker/worker/package_linux64/build/src/typemap.c:190 [inlined]
mtcache_hash_lookup at /buildworker/worker/package_linux64/build/src/typemap.c:251 [inlined]
jl_typemap_intersection_visitor at /buildworker/worker/package_linux64/build/src/typemap.c:526
jl_method_table_insert at /buildworker/worker/package_linux64/build/src/gf.c:1622
_jl_restore_incremental at /buildworker/worker/package_linux64/build/src/dump.c:2174
jl_restore_incremental at /buildworker/worker/package_linux64/build/src/dump.c:3159
_include_from_serialized at ./loading.jl:617
_require_from_serialized at ./loading.jl:684
_require at ./loading.jl:967
require at ./loading.jl:858
require at ./loading.jl:853
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1571 [inlined]
call_require at /buildworker/worker/package_linux64/build/src/toplevel.c:397 [inlined]
eval_import_path at /buildworker/worker/package_linux64/build/src/toplevel.c:432
jl_toplevel_eval_flex at /buildworker/worker/package_linux64/build/src/toplevel.c:630
jl_toplevel_eval_in at /buildworker/worker/package_linux64/build/src/toplevel.c:793
eval at ./boot.jl:328
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
eval_user_input at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:85
macro expansion at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.1/REPL/src/REPL.jl:117 [inlined]
#26 at ./task.jl:259
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2219
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1571 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:572
unknown function (ip: 0xffffffffffffffff)
Allocations: 21554287 (Pool: 21551691; Big: 2596); GC: 40
Aborted (core dumped)

```