2.4/dev/core/src/com/google/gwt/dev/js/ast/JsBinaryOperator.java

/*
 * Copyright 2008 Google Inc.
 * 
 * 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.gwt.dev.js.ast;

/**
 * Represents the operator in a JavaScript binary operation.
 */
public enum JsBinaryOperator implements JsOperator {

  /*
   * Precedence indices from "JavaScript - The Definitive Guide" 4th Edition
   * (page 57)
   * 
   * 
   * Precedence 15 is for really important things that have their own AST
   * classes.
   * 
   * Precedence 14 is for unary operators.
   */

  MUL("*", 13, LEFT | INFIX), DIV("/", 13, LEFT | INFIX), MOD("%", 13, LEFT
      | INFIX),

  ADD("+", 12, LEFT | INFIX), SUB("-", 12, LEFT | INFIX),

  SHL("<<", 11, LEFT | INFIX), SHR(">>", 11, LEFT | INFIX), SHRU(">>>", 11,
      LEFT | INFIX),

  LT("<", 10, LEFT | INFIX), LTE("<=", 10, LEFT | INFIX), GT(">", 10, LEFT
      | INFIX), GTE(">=", 10, LEFT | INFIX), INSTANCEOF("instanceof", 10, LEFT
      | INFIX), INOP("in", 10, LEFT | INFIX),

  EQ("==", 9, LEFT | INFIX), NEQ("!=", 9, LEFT | INFIX), REF_EQ("===", 9, LEFT
      | INFIX), REF_NEQ("!==", 9, LEFT | INFIX),

  BIT_AND("&", 8, LEFT | INFIX),

  BIT_XOR("^", 7, LEFT | INFIX),

  BIT_OR("|", 6, LEFT | INFIX),

  AND("&&", 5, LEFT | INFIX),

  OR("||", 4, LEFT | INFIX),

  // Precedence 3 is for the condition operator.

  // These assignment operators are right-associative.
  ASG("=", 2, INFIX), ASG_ADD("+=", 2, INFIX), ASG_SUB("-=", 2, INFIX), ASG_MUL(
      "*=", 2, INFIX), ASG_DIV("/=", 2, INFIX), ASG_MOD("%=", 2, INFIX), ASG_SHL(
      "<<=", 2, INFIX), ASG_SHR(">>=", 2, INFIX), ASG_SHRU(">>>=", 2, INFIX), ASG_BIT_AND(
      "&=", 2, INFIX), ASG_BIT_OR("|=", 2, INFIX), ASG_BIT_XOR("^=", 2, INFIX),

  COMMA(",", 1, LEFT | INFIX);

  private final int mask;

  private final int precedence;

  private final String symbol;

  private JsBinaryOperator(String symbol, int precedence, int mask) {
    this.symbol = symbol;
    this.precedence = precedence;
    this.mask = mask;
  }

  public int getPrecedence() {
    return precedence;
  }

  public String getSymbol() {
    return symbol;
  }

  public boolean isAssignment() {
    /*
     * Beware, flaky! Maybe I should have added Yet Another Field to
     * BinaryOperator?
     */
    return (getPrecedence() == ASG.getPrecedence());
  }

  public boolean isKeyword() {
    return this == INSTANCEOF || this == INOP;
  }

  public boolean isLeftAssociative() {
    return (mask & LEFT) != 0;
  }

  public boolean isPrecedenceLessThan(JsOperator other) {
    return precedence < other.getPrecedence();
  }

  public boolean isValidInfix() {
    return (mask & INFIX) != 0;
  }

  public boolean isValidPostfix() {
    return (mask & POSTFIX) != 0;
  }

  public boolean isValidPrefix() {
    return (mask & PREFIX) != 0;
  }

  @Override
  public String toString() {
    return symbol;
  }
}