DApp Learnings  –  Storing & Iterating a Collection

I’ve been working on a rock, paper, scissors Ethereum DApp using Solidity, Web3 and the Truffle framework. I hit a few difficulties trying to replicate functionality that would normally be trivial in a non blockchain world so I thought I’d share what I learned.

My first thoughts for the DApp was to display a list of existing games that people had created. Normally if I were doing something like this in Django I’d create a game model and save any new games in the database. To display a list of existing games on the front end I’d query the db and iterate over the returned collection. (I realise storage is expensive when using the Ethereum blockchain but I thought trying to replicate this functionality would make sense and would be a good place to start.)



While investigating the various data types that could be used I found the Typing and Your Contracts Storage page from Ethereum useful. I settled on using a struct, a grouping of variables, stored under one reference.

struct Game {
   string name;
   uint move;
   bool isFinished;
   address ownerAddress;
   uint stake;
   uint index;

That handles one game but I want to store all games. I attempted to do this in a number of different ways but settled on mapping using the games index as the key. Every time a new game is added the index is incremented so I also use gameCount to keep count of the total games.

mapping (uint => Game) games;
uint gameCount;

struct Game {
        string name;
        uint move;
        bool isFinished;
        address ownerAddress;
        uint stake;
        uint index;

To add a new game I used this function:

function StartGame(uint moveId, string gameName) payable {
      require(moveId >= 0 && moveId <= 2);
      games[gameCount].name = gameName;
      games[gameCount].move = moveId;
      games[gameCount].isFinished = false;
      games[gameCount].ownerAddress = msg.sender;
      games[gameCount].stake = msg.value;
      games[gameCount].index = gameCount;

I also added a function that returns the total number of games:

function GetGamesLength() public returns (uint){
   return gameCount;

Returning A Structure

Next I want to be able to get information about a game using it’s index. In Solidity a structure can only be returned by a function from an internal call so for the front end to get the data I had to find another way. I went with the suggestion here — return the fields of the struct as separate return variables.

function GetGame(uint Index) public returns (string, bool, address, uint, uint) {
    return (games[Index].name, games[Index].isFinished, games[Index].ownerAddress, games[Index].stake, games[Index].index);

Front End

On the front end I use Web3 to iterate over each game and display it. To begin I call the GetGamesLength() function. As we saw previously this gives the total number of games. Then I can iterate the index from 0->NoGames to get the data for each game using the GetGame(uint Index) function.

When my page first loads it calls:

getGames: function() {
    var rpsInstance;
    App.contracts.RpsFirst.deployed().then(function(instance) {
      rpsInstance = instance;
      return rpsInstance.GetGamesLength.call();
    }).then(function(gameCount) {
      App.getAllGames(web3.toDecimal(gameCount), rpsInstance);
    }).catch(function(err) {

Web3 – Promises, Promises & more Promises…

The getAllGames function calls GetGame(uint Index) for each game. To do this I created a sequence of promises using the method described here:

getAllGames: function(NoGames, Instance){
   var sequence = Promise.resolve()

   for (var i=0; i < NoGames; i++){(function(){  
         var capturedindex = i
         sequence = sequence.then(function(){
            return Instance.GetGame.call(capturedindex);
            console.log(Game + ' fetched!'
            // Do something with game data. 
            console.log(Game[0]); // Name
            console.log(Game[1]); // isFinished
            console.log('Error loading ' + err)


Looking back at this now it’s all pretty easy looking but it took me a while to get there! I’m still not even sure if it’s the best way to do it. Any advice would be awesome and if it helps someone even better.

Token Models – Storm


Storm are another interesting crypto company that are planning to do an ICO for their Storm Token in the near future so it’s worth investigating how their token model works.

Storm Background

Storm plan to release a number of DApps:

Storm Play: Storm already have a product called BitMaker (1.2M+ downloads across 187 countries) which they are rebranding as Storm Play and integrating to the Storm products.

Storm Market:  A decentralised micro-task marketplace.

Storm Shop: Opportunities where users can learn about or sample retail
goods and services (no real info on this yet).

How It Works

The service is relatively simple, and I see this is as a positive. The basics of the service are described below:

“Makers” and “Players” meet each other to buy and sell tasks.

“Storm Makers,” post tasks using the Storm Play app. To post a task you are required to pay using STORM tokens.

“Storm Players,” use the Storm Play app to perform tasks. Players receive reward units called Bolts in return.

Bolts may not be transferred off of Storm Market but are redeemable for STORM Tokens.

Players can also earn Bolts as part of the gamified reward system (see below). Players can be rewarded for:

  • Creating tasks
  • Completing tasks
  • Managing other Storm Players that a person referred in to complete a task
  • Helping categorize a task or helping to rank a task

These Bolts can be used for boosts. Boosts give the Storm Player access to more micro-tasks for a certain period of time

Token Analysis

As I did the last time, working through the twenty questions proposed by William Mougayar in Tokenomics — A Business Guide to Token Usage, Utility and Value really helps to think about how the tokens are used:

I found it more difficult to answer some of these and I’m not 100% convinced with some of my answers. For now I think the tokens offer the following utility:

The Value Exchange

Players are rewarded Bolts for tasks such as categorising a task or helping to rank a task. These Bolts can be used for boosts. Boosts give the Storm Player access to more micro-tasks for a certain period of time which should lead to more tasks being completed. Think this is maybe clutching a little to meet Mougayars definition, there’s not a real transactional economy between buyers/sellers as there’s not much to spend Bolts on but I think this will develop.

The Toll

Makers are required to pay for posts in STORM tokens. Also Players have to pay Bolts to boost.


The Currency

Reduces traditional payment fees.


Overall score is 9/20. I’m not surprised it’s a fairly low score as my gut feeling is that apart from reducing fees the token isn’t intrinsic to the business plan. Micro-tasks and tokens fit well but they don’t need each other. I do still like the  though and maybe ‘only’ reducing fees is enough – especially with the current industry leaders charging up to 40% (see whitepaper).


Whilst not blockchain technology specific the gamification aspect is interesting and is a big strength for the Storm team so I thought I’d investigate it a bit further in this section.

The main goal of embedding a ‘gamification’ layer to the Storm Market platform is to make it effective in reaching objectives for boosting and delivering business results, like ROE (Return on Engagement). Storm Play can make monotonous work much more enjoyable through a gamified platform.

Unlike previously cited freelance platforms too, gamification is a very important aspect of Storm’s ecosystem. Makers post tasks on the market and Players execute those tasks in exchange of different kinds of rewards (including money) that make the whole thing a fun experience.

To gamify the progression of its users, Storm uses “Bolts” as units of a rewarding system. Users can earn Bolts by doing micro-tasks and by doing training tasks to improve their skills. As their experience increase, they are assigned more micro-tasks. But your experience level on the Storm market is not tied to your Bolts, they are an artifact of it. You can actually use them to get “boosts”: “Within Storm Market, Storm Players can use their balance of Bolts for boosts. Boosts give the Storm Player access to more micro-tasks for a certain period of time”


Storm Website

Analysis of Storm ICO