From ec17e62ed9ac25c546f79cbf09018f9f82a6ed66 Mon Sep 17 00:00:00 2001
From: Takafumi Arakaki <aka.tkf@gmail.com>
Date: Fri, 14 May 2021 04:36:04 -0400
Subject: [PATCH] RFC: Support JuliaFolds interfaces

---
 Project.toml          |  6 +++++-
 src/SentinelArrays.jl |  1 +
 src/folds.jl          | 17 +++++++++++++++++
 test/runtests.jl      | 21 ++++++++++++++++++++-
 4 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 src/folds.jl

diff --git a/Project.toml b/Project.toml
index 73ac73c..6303885 100644
--- a/Project.toml
+++ b/Project.toml
@@ -5,13 +5,17 @@ version = "1.2.16"
 
 [deps]
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
+FGenerators = "4fd0377b-cfdc-4941-97f4-8d7ddbb8981e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
+SplittablesBase = "171d559e-b47b-412a-8079-5efa626c420e"
 
 [compat]
 julia = "1"
 
 [extras]
+Folds = "41a02a25-b8f0-4f67-bc48-60067656b558"
+SplittablesTesting = "3bda5eb5-c32a-4f64-8618-df3be8968470"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Test"]
+test = ["Folds", "SplittablesTesting", "Test"]
diff --git a/src/SentinelArrays.jl b/src/SentinelArrays.jl
index 487227e..c110b0c 100644
--- a/src/SentinelArrays.jl
+++ b/src/SentinelArrays.jl
@@ -451,6 +451,7 @@ end
 
 include("chainedvector.jl")
 include("missingvector.jl")
+include("folds.jl")
 
 include("precompile.jl")
 _precompile_()
diff --git a/src/folds.jl b/src/folds.jl
new file mode 100644
index 0000000..2d226ce
--- /dev/null
+++ b/src/folds.jl
@@ -0,0 +1,17 @@
+using FGenerators: @fgenerator, @yield
+using SplittablesBase: SplittablesBase
+
+@fgenerator(A::ChainedVector) do
+    for array in A.arrays
+        for x in array
+            @yield x
+        end
+    end
+end
+
+function SplittablesBase.halve(A::ChainedVector)
+    chunk = searchsortedfirst(A.inds, length(A) ÷ 2)
+    left = @view A.arrays[1:chunk]
+    right = @view A.arrays[chunk+1:end]
+    return (Iterators.flatten(left), Iterators.flatten(right))
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 842bc6a..e91c121 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,4 +1,4 @@
-using SentinelArrays, Test, Random
+using SentinelArrays, Test, Random, SplittablesTesting, Folds
 
 @testset "SentinelArrays" begin
 
@@ -580,4 +580,23 @@ deleteat!(c2, Int[])
     end
 end
 
+unitrange_chainedvectors = map(1:100) do seed
+    rng = MersenneTwister(seed)
+    ends = cumsum(rand(rng, 0:9, rand(rng, 1:100)))
+    starts = pushfirst!(ends[1:end-1] .+ 1, 1)
+    cv = ChainedVector((:).(starts, ends))
+    return (label = "seed=$seed", data = cv)
+end
+
+@testset "Folds" begin
+    @testset "$label" for (label, data) in unitrange_chainedvectors
+        @test Folds.collect(data, SequentialEx()) == 1:length(data)
+        @test Folds.collect(data) == 1:length(data)
+    end
+end
+
+@testset "SplittablesBase" begin
+    SplittablesTesting.test_unordered(unitrange_chainedvectors)
+end
+
 end