Sunday, July 9, 2017

Scala levels: beginner to expert, application programmer to library designer

This is a good reference for someone who wants to be a library designer. I see that the original website of article (here) is no longer be maintained. So, I put this on my blog so other still can read this. Please enjoy.

Scala is a bit of a chameleon. It makes many programming tasks refreshingly easy and at the same time contains some pretty intricate constructs that allow experts to design truly advanced typesafe libraries. This means that, depending at what piece of code you look at, Scala might look very simple or very complex. But which pieces exactly are easy for beginners and which are more advanced?  In the end, everybody will have their own yardstick. Nevertheless, I am trying here to give a rough categorization.
I hope this will help newcomers to the language decide in what order to pick subjects to learn, and that it will give some advice to teachers and book authors in what order to present the material.
I assume that programmers have already a good knowledge of Java, so we can take at least pre-generics Java 1.4 for granted. If that's not the case, some of the entry-level concepts such as classes and exceptions would need to be moved to more advanced levels.

Also, I distinguish between Scala application programmers and Scala library designers, because the required skill sets are really quite different. A first shot at a categorization has been discussed last month on the scala-debate mailing list.The current categorization incorporates some of the suggestions that were made then. So, here we go:
Level A1: Beginning application programmer
  • Java-like statements and expressions: standard operators, method calls, conditionals, loops, try/catch
  • class, object, def, val, var, import, package
  • Infix notation for method calls
  • Simple closures
  • Collections with map, filter, etc
  • for-expressions
Level A2: Intermediate application programmer
  • Pattern matching
  • Trait composition
  • Recursion, in particular tail recursion
  • XML literals
Level A3: Expert application programmer
  • Folds, i.e. methods such as foldLeft, foldRight
  • Streams and other lazy data structures
  • Actors
  • Combinator parsers
Level L1: Junior library designer
  • Type parameters
  • Traits
  • Lazy vals
  • Control abstraction, currying
  • By-name parameters
Level L2: Senior library designer
  • Variance annotations
  • Existential types (e.g., to interface with Java wildcards)
  • Self type annotations and the cake pattern for dependency injection
  • Structural types (aka static duck typing)
  • Defining map/flatmap/withFilter for new kinds of for-expressions
  • Extractors
Level L3: Expert library designer
  • Early initializers
  • Abstract types
  • Implicit definitions
  • Higher-kinded types
As I wrote above, the skill sets required from application programmers and library designers are really quite different. But if I should throw them into the same baskets, I would group like this:
  • A1, A2/L1, A3/L2, L3
That is, intermediate application programming is about on the same level of difficulty as junior library design, and advanced application programming is on the same level as senior library design.
To clarify: One can program very productively in Scala on level A1, which one should be able to pick up in a day or so, coming from Java. Mastering A2 will doubtlessly increase programmer productivity. A3 is for expert programmers with more specialized tasks, not everyone needs to get to that level. The same holds for library design. There are great libraries designed with the tools on level L1 and L2. Some libraries require L3 elements such as implicits and higher-kinded types, but a library does not automatically get better if it uses these elements -- often the opposite is true.

Sunday, April 30, 2017

Game Development: Text 101 - Text Based Game With Finite State Machine

This time, I've created a really simple text based game that allow the player to progress state to another state by choosing some options. Some options might take the player to the final state of the story and that's where the game end.

A. What I learnt from this course session are:

1. Importing image assets 

To import an image asset, we just need to drag and drop the image from your directory explorer to the asset panel. And if you're working on a 2D game make sure the texture type is "Sprite (2D and UI)" by selecting the image asset in the asset panel and checking the texture type in the inspector.
Unity Game Development - Checking Texture Type in Inspector Panel

2. Adding GameObject to the scene 

In this game, I'm using game object called UI Text. UI Text is an object to display text in the game. To add UI Text: Open Game Object menu -> UI -> Text
Unity Game Development - Adding UI Text GameObject
Unity Game Development - Adding UI Text to Game Scene

3. Toggle layers

In Unity's Game Scene, there are several layers that you can toggle to be visible/invisible. You can find that toggle in the top right corner of Unity.
Unity Game Development - Toggle Layers

4. Canvas

Canvas is where all the game will be operating in. So if you put GameObject such as Text UI outside canvas, that object won't be visible during game play mode.

5. Interacting with GameObjects in Scene Panel 

In the upper-left of unity you can find some useful tools to interact with game object on the scene. Those tools are Hand (Shortcut Q), Move (Shortcut W), Rotate (Shortcut E), Scale (Shortcut R), and UI tool (shortcut T).

Unity Game Development - Tools to Interact with Game Objects

6. Setting camera background color

The camera uses blue as its default background color. We can change it easily just by selecting the Main Camera object in the Hierarchy and change the background color from the inspector panel. In this case, I changed the background color to be black.

7. Add a new component/script to UI Text object

If you want to give your UI text a behavior you can add a script to your game object. One way to add a script is:

1. Select your game object from Hierarchy (In case of my game, it is a UI Text object).
2. Go to your inspector panel and scroll to the bottom. You will find add component button on the bottom.
Unity Game Development - Add Component/Script to Game Object
3. If you want to use existing script, choose "Scipts". But if you want to create new script, choose "New Script".

8. Properties in a assets class will be accessible trough inspector

In order to access your UI Text in your code, you need to create a property in your class for example:

Then to connect your property to the Game Object, you need to select your UI Text object from Hierarchy and then check your inspector (but before that you need to add script to your game object). From the inspector, you'll find a Text Controller (Script) component, and you can set the Text property to the UI Text object as seen in screen capture below.

Unity Game Development - Connecting Text Property to UI Text Game Object

9. There are two main views in Unity (Scene View and Game View)

As you build your game, you can switch from the Scene View to the Game View to preview how it will look in its platform-specific final build. Learn how to preview and test your game as you work. That makes it really fast and easy to try things out.

What are scenes and Game Objects?
You can think of a scene as a level of your game (but it could also be another element, like a main menu, for example). Game Objects are the environment, cameras, lights, and all the other elements in the scene.


  • To get into the center of game object: go to Hierarchy -> double clicks on the game object and you will see your game object in the scene view
  • We can connect game object to the script by creating a public property in the script and then connect that property with GameObject by simply choosing from the inspector.

B. Developing Text 101

In the game development process itself, we are using what we call the Game Design Document (GDD). GDD is a document that outlines our game and its screens. We also learn about Finite-state machine (FSM). FSM is an abstract machine that can be in exactly one of a finite number of states at any given time. It can change from one state to another in response to external inputs.

Game State Diagram

Unity Game Development - State Diagram 1

Unity Game Development - State Diagram 2
In order to transition between states, player need to press a key represent by the state. For example in the first state diagram, player starts in a "cell" state. If the player press "M" key, the player will go to "mirror" state. In code, each state is represented by enum as shown in snippet of code below.

In Update() method, we handle all currentState of the player and create methods to handle the state transition. You might get an idea by looking at this snippet of code.

These are some screenshots of my game. In first screenshot, you can see when the player in the "cell" state and then transitioning to the second state Mirror by pressing M.

Unity Game Development - Player in First "cell" State

Unity Game Development - Player in Second "mirror" State
If you are interested of making this kind of game please take a look at my Github repo below for a complete code:

You can just clone the code and run it on your local machine. I hope you enjoy reading my writing. Can't wait to share more about my game development journey! Thank you.

Game Development: Adding .gitignore File to Unity Repository

I'm using git as my version control for my unity projects. In my second project, I have problem with vast amount of file changes generated by Unity because I forgot to add the .gitignore to my repository. In this post, I want to describe two ways of adding the correct .gitignore file to you unity project's repository.

1. Via Github Web Interface 

When working with my Number Wizard game project, I created the git repository via Github web interface and I can choose to add .gitignore from the Add gitignore dropdown list.

Unity Game Development - .gitignore via Github web interface

2. Add .gitignore For Existing Project

As I mentioned above, in my Text 101 project, I had a problem that git track all Unity's generated files as changes. Each time I changed something in the game scene, it generated thousands tracked changes by git. Here is my solution to that problem:

1. Find the correct gitignore file from this link. For Unity, I'm using this file.

2. Go to your repository folder/directory and create ".gitignore" file in the root of your repo folder.
In windows you can just create and empty file or in Mac you can use "touch .gitignore". In Linux or Mac based system, ".gitignore" file by default would be hidden. You can use "ls -a" to see your file or you can follow this simple tutorial to show hidden files on Mac.

3. Open your empty ".gitignore" file and paste this content and save the change:

4. Run the following commands on you terminal:

  • git rm -r --cached . 
  • git add . 
  • git commit -m ".gitignore is now working"

Please be aware on the first and second commands there is [dot] character there.

Actually this solution works for any gitignore files do you want to add to your repository. If you find this tutorial useful, please leave a comment bellow. Thank you.

Monday, April 3, 2017

Game Development: Text Based Game "Number Wizard"

The online course I've taken were introducing the feature available in Unity using a very simple text based game. The game was called "Number Wizard".

What I learnt from this game were:

  1. How to change the layout of Unity's panels.
  2. Unity's folder structure.
  3. Unity's scene and objects.
  4. How to print logs into Unity's console using print() method.
  5. Unity's game application flow.
    • We can attach a script to an object.
    • That script inherited MonoBehaviour
    • It has Start() method that will be called once in the beginning
    • There is Update() method that will be called once per frame.
  6. How to get input from keyboard.

While all those points are very obvious and basic, I think it is a good start to get to know them all in the beginning of this journey. So it will be a good foundation for me to go faster later.

About Number Wizard

Number Wizard is a game to guess player's number in mind.
Here is the game play of the game:

  1. Player just need to think about one number between 1-10000.
  2. The game will guess with a number.
  3. The player need to answer whether that guess higher, lower, or equal.
  4. If it is still not equal, the game will guess again until find the number of the player have in mind.

The Game implementation

The player can interact with the game using up arrow (tell the guess is higher), down arrow (tell the guess is lower), or space (tell the guess is equal). The game will end if the player press space key. The complete implementation of player's interaction can be seen in line 29-44.

To find the number, we need to implement binary search by calculating the middle value of min and max bound as you can see in FindMid() method in line 64.

You can see the complete project in this  repository of mine:

Please leave comment and suggestion if you find this post interesting. Thank you :)

Wednesday, October 5, 2016

Ubuntu Troubleshoot: Fixing missing and flickering mouse cursor

After fresh install Ubuntu I found that sometimes my mouse cursor is missing and flickering so much. In order to solve this problem we need to disable unknown displays settings as explained below.

1. Open Displays settings from Ubuntu Start Menu.

Open Displays Settings

2. If you are lucky you will see two rectangles shape in the Displays window (red and green). Click on the green colored rectangle with "Unknown Display" on it, as seen below.

Displays Settings "Unknown Display"

3. As you can see in previous image, the Unknown Display is turned on. Click on the switch to turn it off. Then click on "Apply" button.

Turned off Unknown display

That's how I fixed my problem with the mouse cursor. If you find this tips helpful, please leave a comment below. Thank you :)

Ubuntu Tips: Startup Application - Case study enabling touchpad edge scrolling and two fingers scrolling

Today, I want to share a really handy feature in Ubuntu, Startup Application. Startup Application allows you to run additional script or program during the operating system startup. The use case that it can help you are numerous. From mount your drives or devices, startup your development web server, or maybe more complex repetitive tasks that you need to run manually every time you sign into your Ubuntu.

I will show a use case that I personally use in my Ubuntu and this is will be very helpful if you fresh install Ubuntu in your laptop. The use case is to enable edge scrolling and two finger scrolling on your laptop's Synaptics Touchpad. To enable those two features you need to run following commands in your terminal (to open your terminal press ctrl + alt + t):

$ synclient VertEdgeScroll=1 
$ synclient VertTwoFingerScroll=1

If you run those commands you can see that they work perfectly enabled your edge scrolling and two finger scrolling. But the problem is the effect of those commands will wear off every time you restart/shutdown your computer so you need to run those commands again and again. This is the time for Startup Application will help you!

Ok, here is how I use Startup Application:

First Step:
1. Create a bash script called scrolling inside /bin/ directory by running following command in your terminal:

$ sudo gedit /bin/scrolling

2. That command will open a text editor and you need to copy this as its content:

synclient VertEdgeScroll=1 
synclient VertTwoFingerScroll=1

3. Save and close that file.

Second Step:
Make sure you change  the type of that scrolling file into excutable using this command:

$ sudo chmod +x /bin/scrolling

Last Step:
1. Open Startup application from Ubuntu Start menu.

Open Startup Application in Ubuntu
2. Once opened you will see something like this.

View of Startup Application Preferences

3. Click "Add" and enter the following information as in the image below then click "Add".

Name: Scrolling
Command: /bin/scrolling
Comment: Enable two fingers scrolling and edge scrolling

Add Startup Program

4. Close the Startup Application

That's all you have to do, it's easy and you can try restart your computer to see the result. :D

If you find this is helpful or do you have something in mind you want to try with Startup Application? Please share your experience in the comment. Thank you :)

Sunday, August 21, 2016

Copy from dRPC documentation: gRPC Motivation and Design Principles.

I noticed that the motivation and design principles of gRPC is no longer available in the original source. So I copied this documentation for anyone interested in it. Please enjoy.


Google has been using a single general-purpose RPC infrastructure called Stubby to connect the large number of microservices running within and across our data centers for over a decade. Our internal systems have long embraced the microservice architecture gaining popularity today. Having a uniform, cross-platform RPC infrastructure has allowed for the rollout of fleet-wide improvements in efficiency, security, reliability and behavioral analysis critical to supporting the incredible growth seen in that period.

Stubby has many great features - however, it's not based on any standard and is too tightly coupled to our internal infrastructure to be considered suitable for public release. With the advent of SPDY, HTTP/2, and QUIC, many of these same features have appeared in public standards, together with other features that Stubby does not provide. It became clear that it was time to rework Stubby to take advantage of this standardization, and to extend its applicability to mobile, IoT, and Cloud use-cases.

Principles & Requirements

Services not Objects, Messages not References - Promote the microservices design philosophy of coarse-grained message exchange between systems while avoiding the pitfalls of distributed objects and the fallacies of ignoring the network.

Coverage & Simplicity - The stack should be available on every popular development platform and easy for someone to build for their platform of choice. It should be viable on CPU & memory limited devices.

Free & Open - Make the fundamental features free for all to use. Release all artifacts as open-source efforts with licensing that should facilitate and not impede adoption.

Interoperability & Reach - The wire-protocol must be capable of surviving traversal over common internet infrastructure.

General Purpose & Performant - The stack should be applicable to a broad class of use-cases while sacrificing little in performance when compared to a use-case specific stack.

Layered - Key facets of the stack must be able to evolve independently. A revision to the wire-format should not disrupt application layer bindings.

Payload Agnostic - Different services need to use different message types and encodings such as protocol buffers, JSON, XML, and Thrift; the protocol and implementations must allow for this. Similarly the need for payload compression varies by use-case and payload type: the protocol should allow for pluggable compression mechanisms.

Streaming - Storage systems rely on streaming and flow-control to express large data-sets. Other services, like voice-to-text or stock-tickers, rely on streaming to represent temporally related message sequences.

Blocking & Non-Blocking - Support both asynchronous and synchronous processing of the sequence of messages exchanged by a client and server. This is critical for scaling and handling streams on certain platforms.

Cancellation & Timeout - Operations can be expensive and long-lived - cancellation allows servers to reclaim resources when clients are well-behaved. When a causal-chain of work is tracked, cancellation can cascade. A client may indicate a timeout for a call, which allows services to tune their behavior to the needs of the client.

Lameducking - Servers must be allowed to gracefully shut-down by rejecting new requests while continuing to process in-flight ones.

Flow-Control - Computing power and network capacity are often unbalanced between client & server. Flow control allows for better buffer management as well as providing protection from DOS by an overly active peer.

Pluggable - A wire protocol is only part of a functioning API infrastructure. Large distributed systems need security, health-checking, load-balancing and failover, monitoring, tracing, logging, and so on. Implementations should provide extensions points to allow for plugging in these features and, where useful, default implementations.

Extensions as APIs - Extensions that require collaboration among services should favor using APIs rather than protocol extensions where possible. Extensions of this type could include health-checking, service introspection, load monitoring, and load-balancing assignment.

Metadata Exchange - Common cross-cutting concerns like authentication or tracing rely on the exchange of data that is not part of the declared interface of a service. Deployments rely on their ability to evolve these features at a different rate to the individual APIs exposed by services.

Standardized Status Codes - Clients typically respond to errors returned by API calls in a limited number of ways. The status code namespace should be constrained to make these error handling decisions clearer. If richer domain-specific status is needed the metadata exchange mechanism can be used to provide that.

Originally written by Louis Ryan with help from others at Google.

Scala levels: beginner to expert, application programmer to library designer

This is a good reference for someone who wants to be a library designer. I see that the original website of article ( here ) is no longer be...