From 4fbc943b668936b5735245d13b46a31b97de5873 Mon Sep 17 00:00:00 2001
From: Jacob Quinn <quinn.jacobd@gmail.com>
Date: Sun, 28 Jun 2020 12:59:13 -0600
Subject: [PATCH] Fix similar to only return SentinelArray when new type
 includes sentinel type

---
 src/SentinelArrays.jl | 6 +++++-
 test/runtests.jl      | 6 +++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/SentinelArrays.jl b/src/SentinelArrays.jl
index 7598b7d..51e6fe2 100644
--- a/src/SentinelArrays.jl
+++ b/src/SentinelArrays.jl
@@ -114,7 +114,11 @@ Base.convert(::Type{SentinelArray}, arr::AbstractArray{T}) where {T} = convert(S
 Base.convert(::Type{SentinelVector{T}}, arr::AbstractArray) where {T} = convert(SentinelArray{T}, arr)
 
 function Base.similar(A::SentinelArray{T, N, S, V}, ::Type{T2}, dims::Dims{N2}) where {T, N, S, V, T2, N2}
-    SentinelArray{Core.Compiler.typesubtract(T2, V)}(undef, dims)
+    if T2 >: V
+        SentinelArray{Core.Compiler.typesubtract(T2, V)}(undef, dims)
+    else
+        similar(parent(A), T2, dims)
+    end
 end
 
 Base.empty(A::SentinelVector{T}, ::Type{U}=T) where {T, U} = SentinelVector{U}(undef, 0)
diff --git a/test/runtests.jl b/test/runtests.jl
index 400a5c0..d507310 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -35,14 +35,14 @@ y = similar(x, 20)
 y = similar(x, (10, 10))
 @test eltype(parent(x)) == eltype(parent(y))
 @test y[1] === missing
-y = similar(x, Float64)
+y = similar(x, Union{Missing, Float64})
 @test eltype(parent(y)) === Float64
 @test y[1] === missing
-y = similar(x, Float64, 10)
+y = similar(x, Union{Missing, Float64}, 10)
 @test eltype(parent(y)) === Float64
 @test y[1] === missing
 @test length(y) == 10
-y = similar(x, Float64, (10, 10))
+y = similar(x, Union{Missing, Float64}, (10, 10))
 @test eltype(parent(y)) === Float64
 @test y[1] === missing