Method swap

common/expr.h:139–142

  ABSL_MUST_USE_RESULT std::string release_name() { return release(name_); }

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

 private:
  friend class Expr;