specialize for Base.OneTo

Author: jishnub

src/axes.jl

@@ -162,7 +162,13 @@ for f in [:firstindex, :lastindex, :first, :last]
     @eval @inline Base.$f(r::IdOffsetRange) = $f(r.parent) + r.offset
 end
 
-@inline Base.iterate(r::IdOffsetRange, i...) = iterate(UnitRange(r), i...)
+Base.iterate(r::IdOffsetRange, i...) = _iterate(r, i...)
+@inline function _iterate(r::IdOffsetRange, i...)
+    ret = iterate(r.parent, i...)
+    ret === nothing && return nothing
+    return (ret[1] + r.offset, ret[2])
+end
+@inline _iterate(r::IdOffsetRange{<:Integer, <:Base.OneTo}, i...) = iterate(r.parent .+ r.offset, i...)
 
 @propagate_inbounds Base.getindex(r::IdOffsetRange, i::Integer) = r.parent[i - r.offset] + r.offset
 @propagate_inbounds function Base.getindex(r::IdOffsetRange, s::AbstractUnitRange{<:Integer})

test/runtests.jl

@@ -260,12 +260,22 @@ end
         end
     end
     @testset "iteration" begin
+        # parent has Base.OneTo axes
         A = ones(4:10)
         ax = axes(A, 1)
         ind, st = iterate(ax)
         @test A[ind] == A[4]
         ind, st = iterate(ax, st)
         @test A[ind] == A[5]
+
+        # parent doesn't have Base.OneTo axes
+        B = @view A[:]
+        C = OffsetArray(B, 0)
+        ax = axes(C, 1)
+        ind, st = iterate(ax)
+        @test C[ind] == C[4]
+        ind, st = iterate(ax, st)
+        @test C[ind] == C[5]
     end
 end