package org.apache.beam.sdk.values;

import static com.google.common.base.Preconditions.checkArgument;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;

/**
 * Captures a free type variable that can be used in {@link TypeDescriptor#where}. For example:
 *
 * <pre>   {@code
 *   static <T> TypeDescriptor<List<T>> listOf(Class<T> elementType) {
 *     return new TypeDescriptor<List<T>>() {}
 *         .where(new TypeParameter<T>() {}, elementType);
 *   }}</pre>
 */
public abstract class TypeParameter<T> {
  final TypeVariable<?> typeVariable;

  public TypeParameter() {
    Type superclass = getClass().getGenericSuperclass();
    checkArgument(superclass instanceof ParameterizedType, "%s isn't parameterized", superclass);
    typeVariable = (TypeVariable<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0];
  }

  @Override
  public int hashCode() {
    return typeVariable.hashCode();
  }

  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof TypeParameter)) {
      return false;
    }
    TypeParameter<?> that = (TypeParameter<?>) obj;
    return typeVariable.equals(that.typeVariable);
  }

  @Override
  public String toString() {
    return typeVariable.toString();
  }
}

@@ -1,8 +1,814 @@
+/*%0A * Licensed to the Apache Software Foundation (ASF) under one%0A * or more contributor license agreements.  See the NOTICE file%0A * distributed with this work for additional information%0A * regarding copyright ownership.  The ASF licenses this file%0A * to you under the Apache License, Version 2.0 (the%0A * %22License%22); you may not use this file except in compliance%0A * with the License.  You may obtain a copy of the License at%0A *%0A *     http://www.apache.org/licenses/LICENSE-2.0%0A *%0A * Unless required by applicable law or agreed to in writing, software%0A * distributed under the License is distributed on an %22AS IS%22 BASIS,%0A * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.%0A * See the License for the specific language governing permissions and%0A * limitations under the License.%0A */%0A
 package 

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