Method swap

common/expr.h:657–660

  ABSL_MUST_USE_RESULT std::vector<MapExprEntry> release_entries();

  friend void swap(MapExpr& lhs, MapExpr& rhs) noexcept {
    using std::swap;
    swap(lhs.entries_, rhs.entries_);
  }

 private:
  friend class Expr;