sclass PostRequest {
  S url;
  SS params = new LinkedHashMap;
  SS headers = new LinkedHashMap;
  
  *() {}
  *(S *url, O... _) { params = paramsToMap(_); }
  
  S perform() {
    ret doPostWithHeaders(url, headers, params);
  }
  
  selfType set(S param, O value) {
    params.put(param, value);
    this;
  }
}