refactor finding consistent value (#252)

* refactor finding consistent value

* add internal docs

* add doc compat

* remove outdated docstring

* fix inferrability on older julia

docs/Project.toml

@@ -1,6 +1,8 @@
 [deps]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 PooledArrays = "2dfb63ee-cc39-5dd5-95bd-886bf059d720"
+StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 
 [compat]
+Documenter = "0.27"
 PooledArrays = "1"

docs/src/reference.md

@@ -57,4 +57,6 @@ StructArrays.map_params
 StructArrays.buildfromschema
 StructArrays.bypass_constructor
 StructArrays.iscompatible
+StructArrays.maybe_convert_elt
+StructArrays.findconsistentvalue
 ```

src/structarray.jl

@@ -14,12 +14,10 @@ struct StructArray{T, N, C<:Tup, I} <: AbstractArray{T, N}
     components::C
 
     function StructArray{T, N, C}(c) where {T, N, C<:Tup}
-        isempty(c) && error("only eltypes with fields are supported")
-        ax = axes(first(c))
-        length(ax) == N || error("wrong number of dimensions")
-        map(tail(c)) do ci
-            axes(ci) == ax || error("all field arrays must have same shape")
-        end
+        isempty(c) && throw(ArgumentError("only eltypes with fields are supported"))
+        ax = findconsistentvalue(axes, c)
+        (ax === nothing) && throw(ArgumentError("all component arrays must have the same shape"))
+        length(ax) == N || throw(ArgumentError("wrong number of dimensions"))
         new{T, N, C, index_type(c)}(c)
     end
 end
@@ -119,9 +117,6 @@ Construct a `StructArray` from slices of `A` along `dims`.
 The `unwrap` keyword argument is a function that determines whether to
 recursively convert fields of type `FT` to `StructArray`s.
 
-!!! compat "Julia 1.1"
-     This function requires at least Julia 1.1.
-
 ```julia-repl
 julia> X = [1.0 2.0; 3.0 4.0]
 2×2 Array{Float64,2}:
@@ -369,8 +364,8 @@ end
 end
 
 function Base.parentindices(s::StructArray)
-    res = parentindices(component(s, 1))
-    all(c -> parentindices(c) == res, components(s)) || throw(ArgumentError("inconsistent parentindices of components"))
+    res = findconsistentvalue(parentindices, components(s))
+    (res === nothing) && throw(ArgumentError("inconsistent parentindices of components"))
     return res
 end
 

src/utils.jl

@@ -196,3 +196,15 @@ By default, this calls `convert(T, x)`; however, you can specialize it for other
 maybe_convert_elt(::Type{T}, vals) where T = convert(T, vals)
 maybe_convert_elt(::Type{T}, vals::Tuple) where T = T <: Tuple ? convert(T, vals) : vals  # assignment of fields by position
 maybe_convert_elt(::Type{T}, vals::NamedTuple) where T = T<:NamedTuple ? convert(T, vals) : vals # assignment of fields by name
+
+"""
+    findconsistentvalue(f, componenents::Union{Tuple, NamedTuple})
+
+Compute the unique value that `f` takes on each `component ∈ componenents`.
+If not all values are equal, return `nothing`. Otherwise, return the unique value.
+"""
+function findconsistentvalue(f::F, (col, cols...)::Tup) where F
+    val = f(col)
+    isconsistent = mapfoldl(isequal(val)∘f, &, cols; init=true)
+    return ifelse(isconsistent, val, nothing)
+end

test/runtests.jl

@@ -105,6 +105,14 @@ end
     @test StructArrays.strip_params(Tuple{Int}) == Tuple
     @test StructArrays.astuple(NamedTuple{(:a,), Tuple{Float64}}) == Tuple{Float64}
     @test StructArrays.strip_params(NamedTuple{(:a,), Tuple{Float64}}) == NamedTuple{(:a,)}
+
+    cols = (a=rand(2), b=rand(2), c=rand(2))
+    @test StructArrays.findconsistentvalue(length, cols) == 2
+    @test StructArrays.findconsistentvalue(length, Tuple(cols)) == 2
+
+    cols = (a=rand(2), b=rand(2), c=rand(3))
+    @test isnothing(StructArrays.findconsistentvalue(length, cols))
+    @test isnothing(StructArrays.findconsistentvalue(length, Tuple(cols)))
 end
 
 @testset "indexstyle" begin
@@ -439,8 +447,8 @@ end
     @test isequal(t.a, [1, missing])
     @test eltype(t) <: NamedTuple{(:a,)}
 
-    @test_throws ErrorException StructArray([nothing])
-    @test_throws ErrorException StructArray([1, 2, 3])
+    @test_throws ArgumentError StructArray([nothing])
+    @test_throws ArgumentError StructArray([1, 2, 3])
 end
 
 @testset "tuple case" begin
@@ -460,10 +468,10 @@ end
     @test getproperty(t, 1) == [2]
     @test getproperty(t, 2) == [3.0]
 
-    @test_throws ErrorException StructArray(([1, 2], [3]))
+    @test_throws ArgumentError StructArray(([1, 2], [3]))
 
-    @test_throws ErrorException StructArray{Tuple{}}(())
-    @test_throws ErrorException StructArray{Tuple{}, 1, Tuple{}}(())
+    @test_throws ArgumentError StructArray{Tuple{}}(())
+    @test_throws ArgumentError StructArray{Tuple{}, 1, Tuple{}}(())
 end
 
 @testset "constructor from slices" begin
@@ -503,7 +511,7 @@ end
     @test t1 == StructArray((a=[1.2], b=["test"]))
     @test t2 == StructArray{Pair{Float64, String}}(([1.2], ["test"]))
 
-    @test_throws ErrorException StructArray(a=[1, 2], b=[3])
+    @test_throws ArgumentError StructArray(a=[1, 2], b=[3])
 end
 
 @testset "complex" begin