Support IndexStyle, IndexLinear, IndexCartesian

README.md

@@ -101,6 +101,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `bytestring` has been replaced in most cases with additional `String` construction methods; for 0.4 compatibility, the usage involves replacing `bytestring(args...)` with `Compat.String(args...)`. However, for converting a `Ptr{UInt8}` to a string, use the new `unsafe_string(...)` method to make a copy or `unsafe_wrap(String, ...)` to avoid a copy.
 
+* In 0.6, older non-exported indexing traits were renamed and exported as `IndexStyle`, `IndexLinear`, and `IndexCartesian`. Any code specializing `Base.linearindexing(::Type{T})` should switch to `Compat.IndexStyle(::Type{T})`.
+
 ## New functions, macros, and methods
 
 * `@views` takes an expression and converts all slices to views ([#20164]), while

src/Compat.jl

@@ -1384,6 +1384,14 @@ else
     using Base: Iterators
 end
 
+if !isdefined(:IndexStyle)
+    export IndexStyle, IndexLinear, IndexCartesian
+    eval(Expr(:typealias, :IndexStyle, :(Base.LinearIndexing)))
+    eval(Expr(:typealias, :IndexLinear, :(Base.LinearFast)))
+    eval(Expr(:typealias, :IndexCartesian, :(Base.LinearSlow)))
+    IndexStyle{T}(::Type{T}) = Base.linearindexing(T)
+end
+
 include("to-be-deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -1745,4 +1745,18 @@ f20500_2() = A20500_2
 @inferred f20500()
 @inferred f20500_2()
 
+module CompatArray
+using Compat
+immutable CartesianArray{T,N} <: AbstractArray{T,N}
+    parent::Array{T,N}
+end
+immutable LinearArray{T,N} <: AbstractArray{T,N}
+    parent::Array{T,N}
+end
+@compat Compat.IndexStyle(::Type{<:LinearArray}) = IndexLinear()
+end
+@test IndexStyle(Array{Float32,2}) === IndexLinear()
+@test IndexStyle(CompatArray.CartesianArray{Float32,2}) === IndexCartesian()
+@test IndexStyle(CompatArray.LinearArray{Float32,2}) === IndexLinear()
+
 include("to-be-deprecated.jl")