From 40ce5d09224fab03b6ab38f12e9b38d15e08d62a Mon Sep 17 00:00:00 2001
From: Michael Goerz <mail@michaelgoerz.net>
Date: Tue, 24 Feb 2026 17:03:09 -0500
Subject: [PATCH] Add extension for ArrayInterface

---
 Project.toml                                  |  7 +++++++
 ...ntumGradientGeneratorsArrayInterfaceExt.jl | 20 +++++++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 ext/QuantumGradientGeneratorsArrayInterfaceExt.jl

diff --git a/Project.toml b/Project.toml
index 536461a..3d4d4bb 100644
--- a/Project.toml
+++ b/Project.toml
@@ -9,7 +9,14 @@ QuantumControl = "8a270532-f23f-47a8-83a9-b33d10cad486"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 
+[weakdeps]
+ArrayInterface = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"
+
+[extensions]
+QuantumGradientGeneratorsArrayInterfaceExt = "ArrayInterface"
+
 [compat]
+ArrayInterface = "7.0"
 LinearAlgebra = "1"
 QuantumControl = ">=0.11.0"
 Random = "1"
diff --git a/ext/QuantumGradientGeneratorsArrayInterfaceExt.jl b/ext/QuantumGradientGeneratorsArrayInterfaceExt.jl
new file mode 100644
index 0000000..97ca68f
--- /dev/null
+++ b/ext/QuantumGradientGeneratorsArrayInterfaceExt.jl
@@ -0,0 +1,20 @@
+module QuantumGradientGeneratorsArrayInterfaceExt
+
+import ArrayInterface
+import QuantumGradientGenerators: GradVector
+import QuantumControl.QuantumPropagators.Interfaces: supports_vector_interface
+
+# The following methods are necessary for `check_state`, because `similar`
+# can return a `GradVector`, and the results of `similar` must be a mutable
+# array.
+
+ArrayInterface.ismutable(::Type{GradVector{N,T}}) where {N,T} =
+    ArrayInterface.ismutable(T) && supports_vector_interface(T)
+
+
+# Direct access to the elements of a `GradVector` is possible, but should be
+# discouraged
+
+ArrayInterface.fast_scalar_indexing(::Type{<:GradVector}) = false
+
+end