content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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.
   */
  package org.apache.calcite.sql.type;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.SqlOperator;
  import org.apache.calcite.sql.SqlOperatorBinding;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Strategy interface to infer the type of an operator call from the type of the
   * operands.
   *
   * <p>This interface is an example of the
   * {@link org.apache.calcite.util.Glossary#STRATEGY_PATTERN strategy pattern}.
   * This makes
   * sense because many operators have similar, straightforward strategies, such
   * as to take the type of the first operand.
   *
   * @see ReturnTypes
   */
  @FunctionalInterface
  public interface SqlReturnTypeInference {
    //~ Methods ----------------------------------------------------------------
  
    /**
     * Infers the return type of a call to an {@link SqlOperator}.
     *
     * @param opBinding description of operator binding
     * @return inferred type; may be null
     */
    @Nullable RelDataType inferReturnType(
        SqlOperatorBinding opBinding);
  
    /** Returns a return-type inference that applies this rule then a
     * transform. */
    default SqlReturnTypeInference andThen(SqlTypeTransform transform) {
      return ReturnTypes.cascade(this, transform);
    }
  
    /** Returns a return-type inference that applies this rule then another
     * rule, until one of them returns a not-null result. */
    default SqlReturnTypeInference orElse(SqlReturnTypeInference transform) {
      return ReturnTypes.chain(this, transform);
    }
  }
  