add TypeToken<T> to get a T's type in face of type erasure

Author: ktoso

SwiftKit/src/main/java/org/swift/swiftkit/util/TypeToken.java

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package org.swift.swiftkit.util;
+
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+
+/**
+ * Type token to obtain the underlying {@link Type} of a generic type {@code T}.
+ * @param <T>
+ */
+public abstract class TypeToken<T> {
+    private Type type;
+
+    protected TypeToken(){
+        Type superClass = getClass().getGenericSuperclass();
+        this.type = ((ParameterizedType) superClass).getActualTypeArguments()[0];
+    }
+
+    public Type getType() {
+        return type;
+    }
+}

SwiftKit/src/test/java/org/swift/swiftkit/util/TypeTokenTest.java

@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package org.swift.swiftkit.util;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Type;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class TypeTokenTest {
+    @Test
+    void token() {
+        var token = new TypeToken<String>() {};
+        Type type = token.getType();
+        assertEquals(String.class, type);
+    }
+}