Add move-only lambdas support

Bug: 166800618
Test: atest --host android.hardware.biometrics.fingerprint.WorkerThreadTest
Change-Id: I582d44d5098b7426663b75200c822bc6e8bb70a6
diff --git a/biometrics/fingerprint/aidl/default/include/Callable.h b/biometrics/fingerprint/aidl/default/include/Callable.h
new file mode 100644
index 0000000..c629511
--- /dev/null
+++ b/biometrics/fingerprint/aidl/default/include/Callable.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+namespace aidl::android::hardware::biometrics::fingerprint {
+
+// Interface for representing parameterless functions. Unlike std::function<void()>, this can also
+// represent move-only lambdas.
+class Callable {
+  public:
+    virtual void operator()() = 0;
+    virtual ~Callable() = default;
+
+    // Creates a heap-allocated Callable instance from any function object.
+    template <typename T>
+    static std::unique_ptr<Callable> from(T func);
+
+  private:
+    template <typename T>
+    class AnyFuncWrapper;
+};
+
+// Private helper class for wrapping any function object into a Callable.
+template <typename T>
+class Callable::AnyFuncWrapper : public Callable {
+  public:
+    explicit AnyFuncWrapper(T func) : mFunc(std::move(func)) {}
+
+    void operator()() override { mFunc(); }
+
+  private:
+    T mFunc;
+};
+
+template <typename T>
+std::unique_ptr<Callable> Callable::from(T func) {
+    return std::make_unique<AnyFuncWrapper<T>>(std::move(func));
+}
+
+}  // namespace aidl::android::hardware::biometrics::fingerprint
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