Add function abstract_nestedarray_type

Author: oschulz

docs/src/index.md

@@ -8,6 +8,7 @@ This package also defines and exports the following new functions applicable to
 * [`innersize`](@ref) returns the size of the elements of an array, provided they all have equal size.
 * [`deepgetindex`](@ref), [`deepsetindex!`](@ref) and [`deepview`](@ref) provide index-based access across multiple layers of nested arrays
 * [`innermap`](@ref) and [`deepmap`](@ref) apply a function to the elements of the inner (resp. innermost) arrays.
+* [`abstract_nestedarray_type`](@ref) returns the type of nested `AbstractArray`s for a given innermost element type with multiple layers of nesting.
 
 
 ## [ArrayOfSimilarArrays](@id section_ArrayOfSimilarArrays)

src/functions.jl

@@ -198,3 +198,29 @@ Base.@propagate_inbounds _deepview_impl(A::AbstractArray{<:AbstractArray}, idxs_
     _deepview_tupled.(view(A, idxs_outer...), (idxs_inner,))
 
 Base.@propagate_inbounds _deepview_tupled(A::AbstractArray, idxs::Tuple) = deepview(A, idxs...)
+
+
+"""
+    abstract_nestedarray_type(T_inner::Type, ::Val{ndims_tuple})
+
+Return the type of nested `AbstractArray`s. `T_inner` specifies the element
+type of the innermost layer of arrays, `ndims_tuple` specifies the
+dimensionality of each nesting layer (outer arrays first).
+
+If `ndims_tuple` is empty, the returns is the (typically scalar) type
+`T_inner` itself.
+"""
+function abstract_nestedarray_type end
+export abstract_nestedarray_type
+
+
+Base.@pure function abstract_nestedarray_type(::Type{T_inner}, outer::Val{ndims_tuple}) where {T_inner,ndims_tuple}
+    _abstract_nestedarray_type_impl(T_inner, ndims_tuple...)
+end
+
+Base.@pure _abstract_nestedarray_type_impl(::Type{T_inner}) where {T_inner} = T_inner
+
+Base.@pure _abstract_nestedarray_type_impl(::Type{T_inner}, N) where {T_inner} = AbstractArray{T_inner, N}
+
+Base.@pure _abstract_nestedarray_type_impl(::Type{T_inner}, N, M, ndims_tuple...) where {T_inner} =
+    AbstractArray{<:_abstract_nestedarray_type_impl(T_inner, M, ndims_tuple...), N}

test/functions.jl

@@ -62,4 +62,12 @@ using Test
         @test_throws MethodError deepview(B, 6)
         @test_throws MethodError deepview(B, 2, 3)
     end
+
+
+    @testset "abstract_nestedarray_type" begin
+        @test @inferred(abstract_nestedarray_type(Int, Val(()))) == Int
+        @test @inferred(abstract_nestedarray_type(Int, Val((2,)))) == AbstractArray{Int, 2}
+        @test @inferred(abstract_nestedarray_type(Float32, Val((2,3,4)))) ==
+            AbstractArray{<:AbstractArray{<:AbstractArray{Float32, 4}, 3}, 2}
+    end
 end