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;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.type.OperandTypes;
  import org.apache.calcite.sql.type.ReturnTypes;
  import org.apache.calcite.sql.type.SqlOperandTypeChecker;
  import org.apache.calcite.sql.type.SqlOperandTypeInference;
  import org.apache.calcite.sql.type.SqlReturnTypeInference;
  import org.apache.calcite.sql.validate.SqlValidator;
  import org.apache.calcite.sql.validate.SqlValidatorScope;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Generic operator for nodes with internal syntax.
   *
   * <p>If you do not override {@link #getSyntax()} or
   * {@link #unparse(SqlWriter, SqlCall, int, int)}, they will be unparsed using
   * function syntax, {@code F(arg1, arg2, ...)}. This may be OK for operators
   * that never appear in SQL, only as structural elements in an abstract syntax
   * tree.
   *
   * <p>You can use this operator, without creating a sub-class, for
   * non-expression nodes. Validate will validate the arguments, but will not
   * attempt to deduce a type.
   */
  public class SqlInternalOperator extends SqlSpecialOperator {
    //~ Constructors -----------------------------------------------------------
  
    public SqlInternalOperator(
        String name,
        SqlKind kind) {
      this(name, kind, 2);
    }
  
    public SqlInternalOperator(
        String name,
        SqlKind kind,
        int prec) {
      this(name, kind, prec, true, ReturnTypes.ARG0, null, OperandTypes.VARIADIC);
    }
  
    public SqlInternalOperator(
        String name,
        SqlKind kind,
        int prec,
        boolean isLeftAssoc,
        SqlReturnTypeInference returnTypeInference,
        @Nullable SqlOperandTypeInference operandTypeInference,
        SqlOperandTypeChecker operandTypeChecker) {
      super(
          name,
          kind,
          prec,
          isLeftAssoc,
          returnTypeInference,
          operandTypeInference,
          operandTypeChecker);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public SqlSyntax getSyntax() {
      return SqlSyntax.INTERNAL;
    }
  
    @Override public RelDataType deriveType(SqlValidator validator,
        SqlValidatorScope scope, SqlCall call) {
      return validateOperands(validator, scope, call);
    }
  }
  