Undefs.jl is a meant as experimental convenience package and is not meant for production. The convenience constructor, undefs is meant to advance the conversation from recurring calls for a simpler way to allocate arrays without initialization. Additionally, the function undef! and the macro @undef! are highly experimental and use internal details of Julia’s array implementation to unassign elements from arrays of mutable structures.
There’s a Base function for unsetting Array elements, if you don’t want to worry about the internal details yourself (which a prone to changing often). Undefing any other field by unsetting them is undefined behavior, and may lead to miscompilation or program crashes (pun intended)
I encountered a similar problem. From this very interesting discussion, I understand that it is only safe to unset entries in Array (and Memory), not in other structures. I also found jl_arrayunset and Base._unsetindex! but this latter function is neither documented nor public which seems a bit odd as it is used by some Julia packages.
BTW, to solve my problem, I have written a small package, called UnsetIndex.jl, to unset array entries and which has some overlap with Undefs.
UnsetIndex exports two symbols:
a function unsetindex! which calls Base._indexunset! if it exists (Julia version ≥ 1.3) and otherwise calls the C function jl_arrayunset;
a constant unset that is a singleton of a special type for which Base.setindex! and other base methods are extended to achieve similar results as the @undef! macro and more but with a more natural syntax.
To unset an entry of array A at index i, do one of:
The entry is left untouched if it has a bit type. In any case, bound checking is
performed unless @inbounds is active. The only restriction is that A must be of type Array or Memory.
Dot notation is supported. For example:
julia> using UnsetIndex
julia> A = split("This is a wonderful world indeed!")
6-element Vector{SubString{String}}:
"This"
"is"
"a"
"wonderful"
"world"
"indeed!"
julia> A[end] = unset
#undef
julia> A
6-element Vector{SubString{String}}:
"This"
"is"
"a"
"wonderful"
"world"
#undef
julia> A[1:2:5] .= unset
2-element view(::Vector{SubString{String}}, 1:2:3) with eltype SubString{String}:
#undef
#undef
#undef
julia> A
6-element Vector{SubString{String}}:
#undef
"is"
#undef
"wonderful"
#undef
#undef
julia> @. A = unset
6-element Vector{SubString{String}}:
#undef
#undef
#undef
#undef
#undef
#undef
For the last example, A[:] .= unset works as well and I have checked that these two are as fast as explictly writing a loop over all the elements of A.