# Surprising Type Error
**URL:** https://discourse.julialang.org/t/surprising-type-error/51943
**Category:** New to Julia
**Created:** [December 16, 2020, 6:09pm UTC](https://discourse.julialang.org/t/surprising-type-error/51943 "2020-12-16T18:09:42Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@jsundram](https://discourse.julialang.org/u/jsundram)
#### Post date: [December 16, 2020, 6:09pm UTC](https://discourse.julialang.org/t/surprising-type-error/51943/1 "2020-12-16T18:09:42Z")
I ran into the following unexpected error using and array of `CartesianIndex`:
```julia
julia> c = CartesianIndex[]
CartesianIndex[]
julia> push!(c, CartesianIndex(1, 2))
1-element Array{CartesianIndex,1}:
CartesianIndex(1, 2)
julia> M = [1 2; 3 4]
2×2 Array{Int64,2}:
1 2
3 4
julia> M[c]
ERROR: ArgumentError: unable to check bounds for indices of type CartesianIndex{2}
Stacktrace:
[1] checkindex(::Type{Bool}, ::Base.OneTo{Int64}, ::CartesianIndex{2}) at ./abstractarray.jl:561
[2] checkindex at ./abstractarray.jl:576 [inlined]
[3] checkbounds_indices at ./abstractarray.jl:532 [inlined]
[4] checkbounds at ./multidimensional.jl:544 [inlined]
[5] checkbounds at ./abstractarray.jl:506 [inlined]
[6] _getindex at ./multidimensional.jl:742 [inlined]
[7] getindex(::Array{Int64,2}, ::Array{CartesianIndex,1}) at ./abstractarray.jl:1060
[8] top-level scope at REPL[44]:1
```
However, if I iterate over the same array, I get what I expected:
```julia
julia> for x in c
println(M[x])
end
2
```
After some head scratching (and possibly some cursing), I amended the original declaration of c to `c = CartesianIndex{2}[]`, which fixed the problem – `M[c] ` gives the expected result of `2`.
I’m a bit confused by this behavior – can someone explain what’s going on here?
---
### Author:  [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)
#### Post date: [December 16, 2020, 7:06pm UTC](https://discourse.julialang.org/t/surprising-type-error/51943/2 "2020-12-16T19:06:27Z")
Probably there is a `getindex` method for `Array{T, N}` that takes `CartesianIndex{N}[]` (i.e., a `Vector` of concretely typed indexes with the right dimensions) but if the `Vector` is not concretely typed then it probably enters a fallback that errors after.
---
### Author:  [@tobydriscoll](https://discourse.julialang.org/u/tobydriscoll)
#### Post date: [December 21, 2020, 5:03pm UTC](https://discourse.julialang.org/t/surprising-type-error/51943/3 "2020-12-21T17:03:54Z")
Thanks for posting this. Saved me some definite cursing. Not only is this catch/bug obscure, but the error message is almost Kafkaesque.