Make CartesianIndex iterable

Make iterating a CartesianIndex equivalent to iterating the tuple it
holds, being consistent with its indexing behavior.

Author: martinholters

base/multidimensional.jl

@@ -88,6 +88,12 @@ module IteratorsMD
 
     # indexing
     getindex(index::CartesianIndex, i::Integer) = index.I[i]
+    eltype(index::CartesianIndex) = eltype(index.I)
+
+    # iteration
+    start(index::CartesianIndex) = start(index.I)
+    next(index::CartesianIndex, state) = next(index.I, state)
+    done(index::CartesianIndex, state) = done(index.I, state)
 
     # zeros and ones
     zero(::CartesianIndex{N}) where {N} = zero(CartesianIndex{N})

test/arrayops.jl

@@ -1542,6 +1542,8 @@ end
     @test min(CartesianIndex((2,3)), CartesianIndex((5,2))) == CartesianIndex((2,2))
     @test max(CartesianIndex((2,3)), CartesianIndex((5,2))) == CartesianIndex((5,3))
 
+    @test [I1...] == [I1[n] for n in 1:length(I1)]
+
     # CartesianIndex allows construction at a particular dimensionality
     @test length(CartesianIndex{3}()) == 3
     @test length(CartesianIndex{3}(1,2)) == 3