From d5d0279597ce97df623c14bf8e93807313d4afa9 Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <simsurace@gmx.net>
Date: Tue, 6 Feb 2024 11:23:06 +0100
Subject: [PATCH 1/6] Fix type instability

---
 src/flatten.jl | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/flatten.jl b/src/flatten.jl
index 1414cb0..68b6c83 100644
--- a/src/flatten.jl
+++ b/src/flatten.jl
@@ -79,16 +79,20 @@ function flatten(::Type{T}, x::SparseMatrixCSC) where {T<:Real}
 end
 
 function flatten(::Type{T}, x::Tuple) where {T<:Real}
-    x_vecs_and_backs = map(val -> flatten(T, val), x)
-    x_vecs, x_backs = first.(x_vecs_and_backs), last.(x_vecs_and_backs)
-    lengths = map(length, x_vecs)
-    sz = _cumsum(lengths)
+    vec1, back1 = flatten(T, first(x))
+    vec2, back2 = flatten(T, Base.tail(x))
+    l1 = length(vec1)
+    l2 = length(vec2)
     function unflatten_to_Tuple(v::Vector{T})
-        map(x_backs, lengths, sz) do x_back, l, s
-            return x_back(v[(s - l + 1):s])
-        end
+        return (back1(v[1:l1]), back2(v[l1+1:l1+l2]))
     end
-    return reduce(vcat, x_vecs), unflatten_to_Tuple
+    return vcat(vec1, vec2), unflatten_to_Tuple
+end
+
+function flatten(::Type{T}, x::Tuple{}) where {T<:Real}
+    v = T[]
+    unflatten_to_empty_Tuple(::Vector{T}) = x
+    return v, unflatten_to_empty_Tuple
 end
 
 function flatten(::Type{T}, x::NamedTuple) where {T<:Real}

From 4eb267be19fe6b2837e5f5a60a68e0301da2777f Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <simsurace@gmx.net>
Date: Tue, 6 Feb 2024 11:31:00 +0100
Subject: [PATCH 2/6] Fix implementation

---
 src/flatten.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/flatten.jl b/src/flatten.jl
index 68b6c83..3d66fc2 100644
--- a/src/flatten.jl
+++ b/src/flatten.jl
@@ -84,7 +84,7 @@ function flatten(::Type{T}, x::Tuple) where {T<:Real}
     l1 = length(vec1)
     l2 = length(vec2)
     function unflatten_to_Tuple(v::Vector{T})
-        return (back1(v[1:l1]), back2(v[l1+1:l1+l2]))
+        return (back1(v[1:l1]), back2(v[l1+1:l1+l2])...)
     end
     return vcat(vec1, vec2), unflatten_to_Tuple
 end

From b58f524f2869760ea01378e42de7518776697959 Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <simsurace@gmx.net>
Date: Tue, 6 Feb 2024 11:33:28 +0100
Subject: [PATCH 3/6] Add regression test

---
 test/flatten.jl | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/test/flatten.jl b/test/flatten.jl
index 6b15e42..6490062 100644
--- a/test/flatten.jl
+++ b/test/flatten.jl
@@ -39,6 +39,13 @@
         test_flatten_interface((1.0, 2.0); check_inferred=tuple_infers)
 
         test_flatten_interface((1.0, (2.0, 3.0), randn(5)); check_inferred=tuple_infers)
+
+        # Prevent regression of PR #67
+        @testset "Type stability of unflatten" begin
+            θ = (1., ((2., 3.), 4.))
+            x, unflatten = flatten(θ)
+            @test (@inferred unflatten(x)) == θ
+        end
     end
 
     @testset "NamedTuple" begin

From bbc883ae6959ee95e95211ef0790750d350225c6 Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <51025924+simsurace@users.noreply.github.com>
Date: Tue, 6 Feb 2024 11:56:10 +0100
Subject: [PATCH 4/6] Satisfy reviewdog

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 test/flatten.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/flatten.jl b/test/flatten.jl
index 6490062..975cc5e 100644
--- a/test/flatten.jl
+++ b/test/flatten.jl
@@ -42,7 +42,7 @@
 
         # Prevent regression of PR #67
         @testset "Type stability of unflatten" begin
-            θ = (1., ((2., 3.), 4.))
+            θ = (1.0, ((2.0, 3.0), 4.0))
             x, unflatten = flatten(θ)
             @test (@inferred unflatten(x)) == θ
         end

From 7461979a9372741f6921a995f1af34fa3d021c89 Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <51025924+simsurace@users.noreply.github.com>
Date: Tue, 6 Feb 2024 12:01:22 +0100
Subject: [PATCH 5/6] Satisfy reviewdog

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 src/flatten.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/flatten.jl b/src/flatten.jl
index 3d66fc2..08c8f23 100644
--- a/src/flatten.jl
+++ b/src/flatten.jl
@@ -84,7 +84,7 @@ function flatten(::Type{T}, x::Tuple) where {T<:Real}
     l1 = length(vec1)
     l2 = length(vec2)
     function unflatten_to_Tuple(v::Vector{T})
-        return (back1(v[1:l1]), back2(v[l1+1:l1+l2])...)
+        return (back1(v[1:l1]), back2(v[(l1 + 1):(l1 + l2)])...)
     end
     return vcat(vec1, vec2), unflatten_to_Tuple
 end

From f5bdf67cda150d9dd59e6b849760e794dfc7e9d1 Mon Sep 17 00:00:00 2001
From: Simone Carlo Surace <simsurace@gmx.net>
Date: Tue, 6 Feb 2024 18:18:01 +0100
Subject: [PATCH 6/6] Bump version

---
 Project.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index 103aae3..715a381 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ParameterHandling"
 uuid = "2412ca09-6db7-441c-8e3a-88d5709968c5"
 authors = ["Invenia Technical Computing Corporation"]
-version = "0.4.8"
+version = "0.4.9"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"