setindex and promotion

[cossio]

julia> sa = StructArray{Complex}((randn(2), randn(2)));
julia> sa[1] = false
ERROR: type Bool has no field re
Stacktrace:
 [1] getproperty(::Bool, ::Symbol) at ./Base.jl:33
 [2] macro expansion at /home/cossio/.julia/packages/StructArrays/2PoXh/src/utils.jl:46 [inlined]
 [3] foreachfield_gen(::NamedTuple{(:re, :im),Tuple{Array{Float64,1},Array{Float64,1}}}, ::StructArrays.var"#58#59"{Int64}, ::StructArray{Complex,1,NamedTuple{(:re, :im),Tuple{Array{Float64,1},Array{Float64,1}}},Int64}, ::Bool) at /home/cossio/.julia/packages/StructArrays/2PoXh/src/utils.jl:46
 [4] foreachfield(::Function, ::StructArray{Complex,1,NamedTuple{(:re, :im),Tuple{Array{Float64,1},Array{Float64,1}}},Int64}, ::Bool) at /home/cossio/.julia/packages/StructArrays/2PoXh/src/utils.jl:51
 [5] setindex!(::StructArray{Complex,1,NamedTuple{(:re, :im),Tuple{Array{Float64,1},Array{Float64,1}}},Int64}, ::Bool, ::Int64) at /home/cossio/.julia/packages/StructArrays/2PoXh/src/structarray.jl:166
 [6] top-level scope at REPL[21]:1

Compare that with the behavior of normal arrays:

julia> X = randn(2,2) + randn(2,2) * im;
julia> X[1] = false;
julia> X
2×2 Array{Complex{Float64},2}:
      0.0+0.0im        0.872904-2.44604im
 0.300476-0.454121im  -0.156811+0.00139102im

I think StructArray should replicate the behavior of normal arrays, and promote the value being assigned.

[goretkin]

I might have missed this because it's not really about promote but more directly convert.

[fbanning]

Just stumbled upon this issue and the connected issues #182 and PR #184 because I experienced a problem today which I think is similar:

julia> mutable struct A
           id::Int
       end

julia> sa = StructArray{A}(undef, 0)
0-element StructArray(::Vector{Int64}) with eltype A

julia> push!(sa, A(1))
1-element StructArray(::Vector{Int64}) with eltype A:
 A(1)

## getting

julia> sa[1]
A(1)

julia> sa[1].id
1

julia> view(sa, 1).id
0-dimensional view(::Vector{Int64}, 1) with eltype Int64:
1

## setting

julia> sa[1].id = 2 # fails silently
2

julia> sa
1-element StructArray(::Vector{Int64}) with eltype A:
 A(1)

julia> sa.id[1] = 2 # succeeds
2

julia> sa
1-element StructArray(::Vector{Int64}) with eltype A:
 A(2)

Am I right in assuming that these problems are connected? If not, please correct me if I'm wrong. :)

For comparison, here's how it works in a vector of structs:

julia> a = [A(1)]
1-element Vector{A}:
 A(1)

## getting

julia> a[1]
A(1)

julia> a[1].id
1

## setting

julia> a[1].id = 2 # succeeds
2

julia> a
1-element Vector{A}:
 A(2)

I had assumed that typeof(sa[1]) == typeof(a[1]) == A and therefore their reaction to setting properties would be the same.

[piever]

That's actually a separate issue, as the structs are not actually stored (only their fields are), so sa[1] creates the struct on the fly. As a consequence, modifying does not modify the array (see also this comment #181 (comment)).

Maybe that behavior should be documented more thoroughly (documentation PRs welcome!)

[fbanning]

the structs are not actually stored (only their fields are), so sa[1] creates the struct on the fly

I did not know that! Thanks for the answer. :) I will have to look for other ways around this then, maybe LazyRow will do what I hope for.