WIP: allow multiple inputs

docs/src/reference.md

@@ -9,5 +9,6 @@ OffsetArrays.IdOffsetRange
 OffsetArrays.no_offset_view
 OffsetArrays.centered
 OffsetArrays.center
+OffsetArrays.no_offset_view_apply
 OffsetArrays.AxisConversionStyle
 ```

src/OffsetArrays.jl

@@ -298,14 +298,6 @@ if VERSION < v"1.6"
     end
 end
 
-# Utils to translate a function to the parent while preserving offsets
-unwrap(x) = x, identity
-unwrap(x::OffsetArray) = parent(x), data -> OffsetArray(data, x.offsets, checkoverflow = false)
-function parent_call(f, x)
-    parent, wrap_offset = unwrap(x)
-    wrap_offset(f(parent))
-end
-
 Base.similar(A::OffsetArray, ::Type{T}, dims::Dims) where T =
     similar(parent(A), T, dims)
 function Base.similar(A::AbstractArray, ::Type{T}, shape::Tuple{OffsetAxisKnownLength,Vararg{OffsetAxisKnownLength}}) where T
@@ -372,8 +364,8 @@ Base.trues(inds::NTuple{N, Union{Integer, AbstractUnitRange}}) where {N} =
 Base.falses(inds::NTuple{N, Union{Integer, AbstractUnitRange}}) where {N} =
     fill!(similar(BitArray, inds), false)
 
-Base.zero(A::OffsetArray) = parent_call(zero, A)
-Base.fill!(A::OffsetArray, x) = parent_call(Ap -> fill!(Ap, x), A)
+Base.zero(A::OffsetArray) = no_offset_view_apply(zero, A)
+Base.fill!(A::OffsetArray, x) = no_offset_view_apply(Ap -> fill!(Ap, x), A)
 
 ## Indexing
 
@@ -393,7 +385,7 @@ parentindex(r::IdOffsetRange, i) = i - r.offset
 end
 
 @propagate_inbounds Base.getindex(A::OffsetArray{<:Any,N}, c::Vararg{Colon,N}) where N =
-    parent_call(x -> getindex(x, c...), A)
+    no_offset_view_apply(x -> getindex(x, c...), A)
 
 # With one Colon we use linear indexing.
 # In this case we may forward the index to the parent, as the information about the axes is lost
@@ -425,7 +417,7 @@ end
 end
 
 Base.in(x, A::OffsetArray) = in(x, parent(A))
-Base.copy(A::OffsetArray) = parent_call(copy, A)
+Base.copy(A::OffsetArray) = no_offset_view_apply(copy, A)
 
 Base.strides(A::OffsetArray) = strides(parent(A))
 Base.elsize(::Type{OffsetArray{T,N,A}}) where {T,N,A} = Base.elsize(A)
@@ -530,7 +522,7 @@ end
 
 # eltype conversion
 # This may use specialized map methods for the parent
-Base.map(::Type{T}, O::OffsetArray) where {T} = parent_call(x -> map(T, x), O)
+Base.map(::Type{T}, O::OffsetArray) where {T} = no_offset_view_apply(x -> map(T, x), O)
 Base.map(::Type{T}, r::IdOffsetRange) where {T<:Real} = _indexedby(map(T, UnitRange(r)), axes(r))
 if eltype(IIUR) === Int
     # This is type-piracy, but there is no way to convert an IdentityUnitRange to a non-Int type in Base
@@ -634,6 +626,65 @@ _no_offset_view(::Tuple{<:Base.OneTo,Vararg{<:Base.OneTo}}, A::AbstractUnitRange
 _no_offset_view(::Any, A::AbstractArray) = OffsetArray(A, Origin(1))
 _no_offset_view(::Any, A::AbstractUnitRange) = UnitRange(A)
 
+# Utils to translate a function to the parent while preserving offsets
+function unwrap(x, xs...)
+    AT1 = _basetype(typeof(x))
+    all(x->AT1==_basetype(typeof(x)), xs) || throw(ArgumentError("All arrays should be homogeneous, i.e., have the same container type."))
+    _unwrap(x, xs...)
+end
+function _unwrap(x::AT, xs...) where AT<:OffsetArray
+    o = x.offsets
+    all(x->o==x.offsets, xs) || throw(DimensionMismatch("All arrays should have the same offsets."))
+    wrap_offset(data) = OffsetArray(data, o, checkoverflow=false)
+    (parent(x), map(parent, xs)...), wrap_offset
+end
+_unwrap(xs...) = xs, identity
+"""
+    no_offset_view_apply(f, As...) -> C
+
+Apply one-output function `f` to [`no_offset_view`](@ref OffsetArrays.no_offset_view)s of `As` while
+preserve the offsets for its output.
+
+For `OffsetArray`s input, it's almost equivalent to `OffsetArray(f(map(parent, As)...), As[1].offsets)`
+
+# Examples
+
+One can use this to convert the internal array type:
+
+```jldoctest; setup=:(using OffsetArrays)
+Ao = OffsetArray(CartesianIndices((4, 4)), -1, -1);
+parent(Ao) isa Array # false
+
+# collect(Ao): strips the offsets
+# Array(Ao): DimensionMismatch
+dense_Ao = OffsetArrays.no_offset_view_apply(Array, Ao);
+parent(dense_Ao) isa Array
+
+# output
+true
+```
+
+Also, one can do some 1-based mathematics on it:
+
+```jldoctest; setup=:(using OffsetArrays)
+A = OffsetArray(rand(4, 4), -1, -1)
+B = OffsetArray(rand(4, 4), -1, -1)
+
+C = OffsetArrays.no_offset_view_apply(A, B) do x, y
+    x * y
+end
+
+parent(C) == parent(A) * parent(B)
+
+# output
+true
+```
+"""
+function no_offset_view_apply(f, xs...)
+    parent, wrap_offset = unwrap(xs...)
+    wrap_offset(f(parent...))
+end
+
 #####
 # center/centered
 # These two helpers are deliberately not exported; their meaning can be very different in
@@ -702,6 +753,8 @@ instead use [`center`](@ref OffsetArrays.center).
 """
 centered(A::AbstractArray, r::RoundingMode=RoundDown) = OffsetArray(A, .-center(A, r))
 
+# might be available in Base: https://github.com/JuliaLang/julia/issues/35543
+_basetype(::Type{T}) where T = Base.typename(T).wrapper
 
 ####
 # work around for segfault in searchsorted*
@@ -786,7 +839,7 @@ end
 # Adapt allows for automatic conversion of CPU OffsetArrays to GPU OffsetArrays
 ##
 import Adapt
-Adapt.adapt_structure(to, O::OffsetArray) = parent_call(x -> Adapt.adapt(to, x), O)
+Adapt.adapt_structure(to, O::OffsetArray) = no_offset_view_apply(x -> Adapt.adapt(to, x), O)
 
 if Base.VERSION >= v"1.4.2"
     include("precompile.jl")

test/runtests.jl

@@ -864,7 +864,7 @@ end
 @testset "unwrap" begin
     for A in [ones(2, 2), ones(2:3, 2:3), ZeroBasedRange(1:4)]
         p, f = OffsetArrays.unwrap(A)
-        @test f(map(y -> y^2, p)) == A.^2
+        @test f(map(y -> y^2, p...)) == A.^2
     end
 end