# Inconsistent behavior of getindex method with LinearIndices
**URL:** https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041
**Category:** General Usage
**Tags:** indexing
**Created:** [November 1, 2018, 8:25am UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041 "2018-11-01T08:25:48Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@findmyway](https://discourse.julialang.org/u/findmyway)
#### Post date: [November 1, 2018, 8:25am UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041/1 "2018-11-01T08:25:48Z")
Currently we have two `getindex` methods with `LinearIndices` [here](https://github.com/JuliaLang/julia/blob/master/base/indices.jl#L409_L418)
```julia
function getindex(iter::LinearIndices, i::Int)
@_inline_meta
@boundscheck checkbounds(iter, i)
i
end
function getindex(iter::LinearIndices, i::AbstractRange{<:Integer})
@_inline_meta
@boundscheck checkbounds(iter, i)
@inbounds isa(iter, LinearIndices{1}) ? iter.indices[1][i] : (first(iter):last(iter))[i]
end
```
It’s quite strange that the first one just return `i`. I suppose that it should return the `i`th element like the second method. Let’s see the example below:
```julia
julia> iter = LinearIndices((-1:1,))
3-element LinearIndices{1,Tuple{UnitRange{Int64}}}:
1
2
3
julia> iter[2:2]
0:0
julia> iter[2]
2
```
---
### Author:  [@oliver](https://discourse.julialang.org/u/oliver)
#### Post date: [November 1, 2018, 8:03pm UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041/2 "2018-11-01T20:03:00Z")
```julia
julia> iter[2,:,]
2
```
---
### Author:  [@findmyway](https://discourse.julialang.org/u/findmyway)
#### Post date: [November 1, 2018, 11:44pm UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041/3 "2018-11-01T23:44:57Z")
Yeah, I know, this will fallback to `AbstractArray`’s default `getindex` implementation. My key point here is why `LinearIndices` here choose to not support negative `UnitRange`.
Seems `CartesianIndices` supports it well:
```julia
julia> inds = CartesianIndices((-1:1, -1:1))
3×3 CartesianIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}:
CartesianIndex(-1, -1) CartesianIndex(-1, 0) CartesianIndex(-1, 1)
CartesianIndex(0, -1) CartesianIndex(0, 0) CartesianIndex(0, 1)
CartesianIndex(1, -1) CartesianIndex(1, 0) CartesianIndex(1, 1)
julia> inds[1]
CartesianIndex(-1, -1)
julia> iter = LinearIndices((-1:1, -1:1))
3×3 LinearIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}:
1 4 7
2 5 8
3 6 9
julia> iter[CartesianIndex(-1,-1)]
ERROR: BoundsError: attempt to access 3×3 LinearIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}} at index [-1, -1]
Stacktrace:
[1] throw_boundserror(::LinearIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}, ::Tuple{Int64,Int64}) at .\abstractarray.jl:484
[2] checkbounds at .\abstractarray.jl:449 [inlined]
[3] _getindex at .\abstractarray.jl:927 [inlined]
[4] getindex(::LinearIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}, ::CartesianIndex{2}) at .\abstractarray.jl:905
[5] top-level scope at none:0
```
If the aim of `LinearIndices` and `CartesianIndices` is to provide conversion between each other, then I suppose this error should not happen(the last one is supposed to return `1`, I guess?).
---
### Author:  [@oliver](https://discourse.julialang.org/u/oliver)
#### Post date: [November 2, 2018, 4:53am UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041/4 "2018-11-02T04:53:58Z")
```julia
julia> inds[CartesianIndex(-1, 1)]
ERROR: BoundsError: attempt to access 3×3
CartesianIndices{2,Tuple{UnitRange{Int64},UnitRange{Int64}}}
at index [-1, 1]
```
---
### Author:  [@findmyway](https://discourse.julialang.org/u/findmyway)
#### Post date: [November 2, 2018, 7:18am UTC](https://discourse.julialang.org/t/inconsistent-behavior-of-getindex-method-with-linearindices/17041/5 "2018-11-02T07:18:46Z")
Thanks!
It’s my fault.