From 47e496f8bdae00fac236f53bf7cc2090954b9f3d Mon Sep 17 00:00:00 2001
From: Tim Holy <tim.holy@gmail.com>
Date: Fri, 13 Jul 2018 12:35:10 -0500
Subject: [PATCH] Define promotion and conversion for CartesianIndices and
 LinearIndices (#28084)

---
 base/indices.jl          | 11 +++++++++++
 base/multidimensional.jl |  8 +++++++-
 test/abstractarray.jl    |  8 ++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/base/indices.jl b/base/indices.jl
index 5e1c858d87781..84830137db5c8 100644
--- a/base/indices.jl
+++ b/base/indices.jl
@@ -357,6 +357,17 @@ LinearIndices(inds::NTuple{N,Union{<:Integer,AbstractUnitRange{<:Integer}}}) whe
     LinearIndices(map(i->first(i):last(i), inds))
 LinearIndices(A::Union{AbstractArray,SimpleVector}) = LinearIndices(axes(A))
 
+promote_rule(::Type{LinearIndices{N,R1}}, ::Type{LinearIndices{N,R2}}) where {N,R1,R2} =
+    LinearIndices{N,indices_promote_type(R1,R2)}
+
+function indices_promote_type(::Type{Tuple{R1,Vararg{R1,N}}}, ::Type{Tuple{R2,Vararg{R2,N}}}) where {R1,R2,N}
+    R = promote_type(R1, R2)
+    Tuple{R,Vararg{R,N}}
+end
+
+convert(::Type{LinearIndices{N,R}}, inds::LinearIndices{N}) where {N,R} =
+    LinearIndices(convert(R, inds.indices))
+
 # AbstractArray implementation
 IndexStyle(::Type{<:LinearIndices}) = IndexLinear()
 axes(iter::LinearIndices) = map(axes1, iter.indices)
diff --git a/base/multidimensional.jl b/base/multidimensional.jl
index fd8e8024e8b59..5fe078a47ca41 100644
--- a/base/multidimensional.jl
+++ b/base/multidimensional.jl
@@ -4,7 +4,7 @@
 module IteratorsMD
     import .Base: eltype, length, size, first, last, in, getindex,
                  setindex!, IndexStyle, min, max, zero, one, isless, eachindex,
-                 ndims, IteratorSize, convert, show, iterate
+                 ndims, IteratorSize, convert, show, iterate, promote_rule
 
     import .Base: +, -, *
     import .Base: simd_outer_range, simd_inner_length, simd_index
@@ -228,6 +228,9 @@ module IteratorsMD
 
     CartesianIndices(A::AbstractArray) = CartesianIndices(axes(A))
 
+    promote_rule(::Type{CartesianIndices{N,R1}}, ::Type{CartesianIndices{N,R2}}) where {N,R1,R2} =
+        CartesianIndices{N,Base.indices_promote_type(R1,R2)}
+
     convert(::Type{Tuple{}}, R::CartesianIndices{0}) = ()
     convert(::Type{NTuple{N,AbstractUnitRange{Int}}}, R::CartesianIndices{N}) where {N} =
         R.indices
@@ -246,6 +249,9 @@ module IteratorsMD
     convert(::Type{Tuple{Vararg{UnitRange}}}, R::CartesianIndices) =
         convert(Tuple{Vararg{UnitRange{Int}}}, R)
 
+    convert(::Type{CartesianIndices{N,R}}, inds::CartesianIndices{N}) where {N,R} =
+        CartesianIndices(convert(R, inds.indices))
+
     # AbstractArray implementation
     Base.axes(iter::CartesianIndices{N,R}) where {N,R} = map(Base.axes1, iter.indices)
     Base.IndexStyle(::Type{CartesianIndices{N,R}}) where {N,R} = IndexCartesian()
diff --git a/test/abstractarray.jl b/test/abstractarray.jl
index 36cfc8704ad1c..aff3e78e718ed 100644
--- a/test/abstractarray.jl
+++ b/test/abstractarray.jl
@@ -887,6 +887,14 @@ end
 
     @test CartesianIndices(fill(1., 2, 3)) == CartesianIndices((2,3))
     @test LinearIndices((2,3)) == [1 3 5; 2 4 6]
+
+    for IType in (CartesianIndices, LinearIndices)
+        I1 = IType((Base.OneTo(3),))
+        I2 = IType((1:3,))
+        @test !(I1 === I2)
+        J1, J2 = @inferred(promote(I1, I2))
+        @test J1 === J2
+    end
 end
 
 @testset "issue #25770" begin