src/main/java/com/google/devtools/build/lib/syntax/Token.java

// Copyright 2014 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 Token represents an actual lexeme; that is, a lexical unit, its location in
 * the input text, its lexical kind (TokenKind) and any associated value.
 */
class Token {

  TokenKind kind;
  int left;
  int right;
  /**
   * value is an Integer if the kind is INT.
   * It is a String if the kind is STRING, IDENTIFIER, or COMMENT.
   * It is null otherwise.
   */
  @Nullable Object value;

  Token(TokenKind kind, int left, int right) {
    this(kind, left, right, null);
  }

  Token(TokenKind kind, int left, int right, Object value) {
    this.kind = kind;
    this.left = left;
    this.right = right;
    this.value = value;
  }

  Token copy() {
    return new Token(kind, left, right, value);
  }

  /**
   * Constructs an easy-to-read string representation of token, suitable for use
   * in user error messages.
   */
  @Override
  public String toString() {
    // TODO(bazel-team): do proper escaping of string literals
    return kind == TokenKind.STRING     ? ("\"" + value + "\"")
        : value == null                 ? kind.getPrettyName()
        : value.toString();
  }

}