Class StringIterator

java/com/google/re2j/Parser.java:706–783

  //   lookingAt().
  // Only use pop() to advance over possibly non-ASCII runes.
  private static class StringIterator {
    private final String str; // a stream of UTF-16 codes
    private int pos = 0; // current position in UTF-16 string

    StringIterator(String str) {
      this.str = str;
    }

    // Returns the cursor position.  Do not interpret the result!
    int pos() {
      return pos;
    }

    // Resets the cursor position to a previous value returned by pos().
    void rewindTo(int pos) {
      this.pos = pos;
    }

    // Returns true unless the stream is exhausted.
    boolean more() {
      return pos < str.length();
    }

    // Returns the rune at the cursor position.
    // Precondition: |more()|.
    int peek() {
      return str.codePointAt(pos);
    }

    // Advances the cursor by |n| positions, which must be ASCII runes.
    //
    // (In practise, this is only ever used to skip over regexp
    // metacharacters that are ASCII, so there is no numeric difference
    // between indices into  UTF-8 bytes, UTF-16 codes and runes.)
    void skip(int n) {
      pos += n;
    }

    // Advances the cursor by the number of cursor positions in |s|.
    void skipString(String s) {
      pos += s.length();
    }

    // Returns the rune at the cursor position, and advances the cursor
    // past it.  Precondition: |more()|.
    int pop() {
      int r = str.codePointAt(pos);
      pos += Character.charCount(r);
      return r;
    }

    // Equivalent to both peek() == c but more efficient because we
    // don't support surrogates.  Precondition: |more()|.
    boolean lookingAt(char c) {
      return str.charAt(pos) == c;
    }

    // Equivalent to rest().startsWith(s).