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// Copyright 2020 The Bazel Authors. All rights reserved.
//
// 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.
package com.google.devtools.build.lib.syntax;
import javax.annotation.Nullable;
/**
* A Starlark value that supports binary operators such as {@code x+y}.
*
* <p>During evaluation of a Starlark binary operation, if none of the built-in cases match, then
* the left operand is queried; if it implements HasBinary, its {@link #binaryOp} method is called.
* If the left operand does not implement HasBinary, or declines to implement the particular
* operation by returning null, then the right operand is queried for HasBinary and its {@link
* #binaryOp} method is called. If neither operand defines the operator, evaluation fails.
*
* <p>Subclasses should strive for appropriate symmetries in their implementations, such as {@code x
* * y == y * x}.
*/
// TODO(adonovan): rename BinaryOperand?
public interface HasBinary extends StarlarkValue {
/**
* Returns {@code this op that}, if thisLeft, or {@code that op this} otherwise. May return null
* to indicate that the operation is not supported, or may throw a specific exception.
*/
@Nullable
Object binaryOp(TokenKind op, Object that, boolean thisLeft) throws EvalException;
}