# BoundsError when NullableArray a field
**URL:** https://discourse.julialang.org/t/boundserror-when-nullablearray-a-field/3084
**Category:** General Usage
**Created:** [April 6, 2017, 9:14am UTC](https://discourse.julialang.org/t/boundserror-when-nullablearray-a-field/3084 "2017-04-06T09:14:04Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@merl-dev](https://discourse.julialang.org/u/merl-dev)
#### Post date: [April 6, 2017, 9:14am UTC](https://discourse.julialang.org/t/boundserror-when-nullablearray-a-field/3084/1 "2017-04-06T09:14:05Z")
(Posted originally as [NullableArrays issue #190](https://github.com/JuliaStats/NullableArrays.jl/issues/190), likely should have started here on discourse before filing an issue…)
Not sure if I missed something about iteration interfaces or `NullableArrays`, but consider the following (valid for NullableArrays 0.1.0 and master, julia v0.5.1 and 0.6.0-pre.beta.14, on ubuntu 14):
```julia
julia> type A
arr::Array{String}
end
julia> a = A(String[])
A(String[])
julia> start(a.arr)
1
julia> done(a.arr, 1)
true
julia> using NullableArrays
julia> type B
arr::NullableArray{String}
end
julia> b = B(NullableArray{String}[])
B(Nullable{String}[])
julia> start(b.arr)
(Base.OneTo(0), 1)
julia> done(b.arr, 1)
ERROR: BoundsError
Stacktrace:
[1] getindex at ./number.jl:38 [inlined]
[2] done(::NullableArrays.NullableArray{String,1}, ::Int64) at ./abstractarray.jl:753
```
To be sure, when NullableArray is not a field:
```julia
julia> c = NullableArray{String}[]
0-element Array{NullableArrays.NullableArray{String,N} where N,1}
julia> start(c)
1
julia> done(c, 1)
true
```
---
### Author:  [@Dan](https://discourse.julialang.org/u/Dan)
#### Post date: [April 6, 2017, 3:16pm UTC](https://discourse.julialang.org/t/boundserror-when-nullablearray-a-field/3084/2 "2017-04-06T15:16:05Z")
Note that `c` is an Array of NullableArrays of Strings, and not a NullableArray of Strings which is more expected. As a regular Array, the `start` returns an integer position.
`b.arr` is a NullableArray of Strings, and as `start` is not defined for NullableArrays, it goes to AbstractArray definition which returns the range. To check if `done`, one needs to pass the state of the iterator which in `b.arr`’s case is the tuple `(Base.OneTo(0), 1)` and indeed `done(b.arr,(Base.OneTo(0), 1))` is `true`.
The confusion may be the result of the `[]` in the construction, which creates an array. The `type B` constructor has to force the `Nullable{String}` type on `arr` and uses `convert(NullableArray{String},NullableArray{String}[])` which works because the converted array is empty.
Conclusion, probably a typo, but perhaps Julia syntax dynamism is getting confusing.
---
### Author:  [@merl-dev](https://discourse.julialang.org/u/merl-dev)
#### Post date: [April 6, 2017, 3:52pm UTC](https://discourse.julialang.org/t/boundserror-when-nullablearray-a-field/3084/3 "2017-04-06T15:52:07Z")
I wish it were a typo 😊, just some bad habits when creating empty arrays. Thanks for the clarification.