Preserve offsets on broadcasting IdOffsetRange (#114)

Author: yha

src/axes.jl

@@ -158,6 +158,14 @@ end
     return IdOffsetRange(r.parent[s .- r.offset], r.offset)
 end
 
+# offset-preserve broadcasting
+Broadcast.broadcasted(::Base.Broadcast.DefaultArrayStyle{1}, ::typeof(-), r::IdOffsetRange{T}, x::Integer) where T =
+    IdOffsetRange{T}(r.parent .- x, r.offset)
+Broadcast.broadcasted(::Base.Broadcast.DefaultArrayStyle{1}, ::typeof(+), r::IdOffsetRange{T}, x::Integer) where T =
+    IdOffsetRange{T}(r.parent .+ x, r.offset)
+Broadcast.broadcasted(::Base.Broadcast.DefaultArrayStyle{1}, ::typeof(+), x::Integer, r::IdOffsetRange{T}) where T =
+    IdOffsetRange{T}(x .+ r.parent, r.offset)
+
 Base.show(io::IO, r::IdOffsetRange) = print(io, first(r), ':', last(r))
 
 # Optimizations

test/runtests.jl

@@ -73,6 +73,11 @@ using CatIndices: BidirectionalVector
     @test @inferred(oftype(ro, 1:2)) === OffsetArrays.IdOffsetRange(Base.OneTo(2))
     @test_broken try oftype(ro, 3:4); false catch err true end
     # @test_throws ArgumentError oftype(ro, 3:4)
+
+    # broadcasting behavior with scalars (issue #104)
+    r3 = (1 .+ OffsetArrays.IdOffsetRange(3:5, -1) .+ 1) .- 1
+    @test same_value(r3, 3:5)
+    check_indexed_by(r3, 0:2)
 end
 
 @testset "Single-entry arrays in dims 0:5" begin