From c52ac88e27c4fbe2fc26d5583f907c494032736b Mon Sep 17 00:00:00 2001
From: Nicholas Bauer <nicholasbauer@outlook.com>
Date: Tue, 17 Sep 2024 09:55:45 -0400
Subject: [PATCH] Make NoTangent have an eltype of itself.

---
 src/tangent_types/abstract_zero.jl  | 2 ++
 test/tangent_types/abstract_zero.jl | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/src/tangent_types/abstract_zero.jl b/src/tangent_types/abstract_zero.jl
index 6838168af..c5260489e 100644
--- a/src/tangent_types/abstract_zero.jl
+++ b/src/tangent_types/abstract_zero.jl
@@ -93,6 +93,8 @@ end
 """
 struct NoTangent <: AbstractZero end
 
+Base.eltype(::Type{NoTangent}) = NoTangent
+
 """
     zero_tangent(primal)
 
diff --git a/test/tangent_types/abstract_zero.jl b/test/tangent_types/abstract_zero.jl
index 94df8e2ac..85a9e1d07 100644
--- a/test/tangent_types/abstract_zero.jl
+++ b/test/tangent_types/abstract_zero.jl
@@ -119,6 +119,9 @@
         @test dot(dne, 17.2) == dne
         @test dot(11.9, dne) == dne
 
+        @test eltype(dne) === NoTangent
+        @test eltype(NoTangent) === NoTangent
+
         @test promote_type(NoTangent, Bool) == Bool
         @test promote_type(Bool, NoTangent) == Bool
         @test promote_type(NoTangent, Int64) == Int64