Method concat

java/com/google/re2j/Parser.java:260–272

()

  // concat replaces the top of the stack (above the topmost '|' or '(') with
  // its concatenation.
  private Regexp concat() {
    maybeConcat(-1, 0);

    // Scan down to find pseudo-operator | or (.
    Regexp[] subs = popToPseudo();

    // Empty concatenation is special case.
    if (subs.length == 0) {
      return push(newRegexp(Regexp.Op.EMPTY_MATCH));
    }

    return push(collapse(subs, Regexp.Op.CONCAT));
  }

  // alternate replaces the top of the stack (above the topmost '(') with its
  // alternation.