Software Engineering Thailand: Programming with Scala

Programming with ScalaBrian Topping

Mauswerks LLC

About Me• Globally experienced dev with over 25 years professional experience

• Have led teams of three to fifteen developers as lead developer, architect, general manager. Start projects first, then hire when ten fingers are not enough.

• Have been using Scala since 2012, JDK Open Source since 2001

• Interests: Functional Reactive Programming, financial markets, machine learning, Javascript, travel, motorcycles

• Shameless plug: Available for investment or work in BKK

• http://github.com/briantoppinghttp://twitter.com/briantoppinghttp://linkedin.com/in/briantopping

https://github.com/briantopping

http://twitter.com/briantopping

http://linkedin.com/in/briantopping

Why Scala?

What is wrong with this picture?

• "Looks good to me, ship it!"


• We're at the wrong level of zoom to see problems



•



•

• Solutions at a global level must factor problems at the local level.



•

• Solutions at a global level must factor problems at the local level.

• Complexity is the natural tradeoff

What is Scala?

• Object Oriented / Functional hybrid

• Compiled to JVM bytecode

• Statically typed (compile time)

• Strongly typed (types must match)

• Growing ecosystem

• Language is stable and mature

(a few) Benefits of Scala

• Seamless Java / JDK ecosystem interoperability

• Type Inferencing & Parameterization

• Concurrency & Distribution

• Collections Classes

• Pattern Matching

• Obvious Correctness

Standard Example

Standard Example

• Java "Bean"

Standard Example

• Java "Bean"

• Scala Case Class

Java / JDK Interoperability


• Scala classes are JVM classes



• Groovy, Clojure, JRuby, Jython – 40+ in all!




• Scala is a mixed Object + Functional language





• It is possible and common for young teams to start writing Scala with Java style (OOD) and API, test with existing tools





• It is possible and common for young teams to start writing Scala with Java style (OOD) and API, test with existing tools

• Take advantage of Java libraries

Type Inference & Immutability Focus


• Compiler knows the type of an assignment, yet most languages require the developer to prove it



• Java:



• Java:

• Scala:



• Java:

• Scala:

• Built for immutability!



• Java:

• Scala:


• Use the var keyword for mutable variables



• Java:

• Scala:


• Use the var keyword for mutable variables

• One finds themselves using it less and less often!

Type Parameterization

Type Parameterization• Types allow you to denote function domain & codomains. For example, from

mathematics, we are used to seeing:this tells us that function “f” maps values from the set of real numbers to values of the set of natural numbers

http://twitter.github.io/scala_school/type-basics.html



• In the abstract, this is exactly what concrete types are. Type systems give us some more powerful ways to express these sets





• Given these annotations, the compiler can now statically (at compile time) verify that the program is sound






• Variance annotations allow you to express relationships between class hierarchies & polymorphic types






• Variance annotations allow you to express relationships between class hierarchies & polymorphic types

• Reference: http://twitter.github.io/scala_school/type-basics.html


Concurrency & Distribution

Concurrency & Distribution• Futures and Promises – Long history across platforms


• Factory objects look like integral part of language



• Remember that functions are parameters!




•




•

• Don't return values, return a Future!




•


• Akka-HTTP is a perfect example, you can return a value, but then your code manages the concurrency. Return a Future to the caller and let it manage it instead!




•


• Akka-HTTP is a perfect example, you can return a value, but then your code manages the concurrency. Return a Future to the caller and let it manage it instead!

• Unlike Node, full access to all cores.

Collections Classes

Collections Classes• Scala Collections are what brought me to the language


• Designed to consistently behave as a collections DSL



• Immutable by default, great for parallel deployments




• Java




• Java

•




• Java

•

• Scala




• Java

•

• Scala

•




• Java

•

• Scala

•

• Don't get the wrong idea here! Rolling a one-liner into a println is not what I'd call "good style". Instead, note how the functional transparency and type inferencing allows us to inline functions as easily as we can assign them to variables.

Pattern Matching

Pattern Matching

• Partial Functions – A function that is only defined for specific input values

Pattern Matching


•

Pattern Matching


•

• Regular Expressions – Please enjoy them now! 😉

Pattern Matching


•

• Regular Expressions – Please enjoy them now! 😉

•

Obvious Correctness

Obvious Correctness• Trick question: Which of these is more obviously correct?


• Java:


• Java:

• Scala:


• Java:

• Scala:

• Depends on experience!!

Team Evolution w/ Scala


• Start with this:



• To get to this:



• To get to this:

• Make the transition gradually! Do it together as a team!

What does all this buy us?

What does all this buy us?• Pure functions have no side effects... data in, data out


• Objects maintain state. This is why Scala is not considered a purely functional language!



• When objects are immutable though, the state acts as constants in the functions. Constants are thread-safe!




• Immutable objects do not need to be locked. Locking is actually very expensive and error prone




• Immutable objects do not need to be locked. Locking is actually very expensive and error prone

• Immutable state is updated by replacing the object!

But it looks so complex!

But it looks so complex!• Scala actually has a smaller grammar than Java


• Functional composition (the ability for one function to feed another) allows intermediate variables to be removed.



• Scala ends up looking complex because developers collapse code that maybe shouldn't be collapsed.




• Program so your code is readable, not so it fits in as few lines as possible.




• Program so your code is readable, not so it fits in as few lines as possible.

• Occam's Razor: We should reduce to the simplest possible outcome, and no simpler!

Some things haven't changed

Some things haven't changed• TDD – Use it! Create unit tests for everything, use them as documentation


• One liners should have a simple comment describing what they do



• Frequent code reviews! Pull requests that receive no comments are to be avoided.




• Avoid learning a new technique and immediately using it everywhere.





• If you are the only person that can maintain your code, you will be cursed to own it forever.





• If you are the only person that can maintain your code, you will be cursed to own it forever.

• If you can inspire others to read your code because it is both short and people "learn one new thing" (only one!), you will be able to move the team forward with new techniques, do more with less, have fun!

I'm not sold yet...

I'm not sold yet...

• Take Coursera's Scala class taught by Martin Odersky

I'm not sold yet...


• You will become a better Scala programmer

I'm not sold yet...



• You will become a better Java programmer

I'm not sold yet...




• You will become a better programmer

I'm not sold yet...





• Apple's Swift language is a bit of a knockoff

I'm not sold yet...





• Apple's Swift language is a bit of a knockoff

• Get two platforms for the price of one!

How Do I Get Started?

IDEs: IntelliJ vs. Eclipse


• They both have advantages. Each team should "bake off" and doc the results


• They both have advantages. Each team should "bake off" and doc the results

• Don't be restricted to one, but a common denominator of skills is helpful

Testing

Testing• ScalaTest is standard


• Behavior Driven Development



• Use with TDD, just works!



• Use with TDD, just works!

• The power is in the Matchers

Development Environments

Development Environments• REPL (Read-Eval-Print Loop) is an interactive shell


• scalac compiler can be run from command line like javac



• SBT is Scala's own build tool, allows Scala code to be used within build, but not very IDE friendly.




• Maven has a Scala plugin, but comes with all of Maven's idiosyncrasies.





• SBT can use Maven central repository, but is designed for Ivy repositories. Both end up being required, which is a pain point.






• All the cool kids use SBT, but it's not as mature and harder to use with projects that span multiple source repositories, also not as simple for tagged release environments.






• All the cool kids use SBT, but it's not as mature and harder to use with projects that span multiple source repositories, also not as simple for tagged release environments.

• Verdict: If you already use Maven, stick with it, otherwise use SBT.

Concurrency & Distribution Part 2


• Use Akka – http://akka.io

http://akka.io



• Scala and Java APIs, Scala easier to use via immutables

http://akka.io




• Message passing pattern without all the JMS overhead

http://akka.io





• 50 million msg/sec on a single machine + small memory footprint; ~2.5 million actors (message endpoints) per GB of heap

http://akka.io






• Remoting can scale to tens of thousands of machines

http://akka.io







• Akka Streams focuses on streaming messages, uses standard TCP facilities to throttle clients, avoid buffer overflows

http://akka.io







• Akka Streams focuses on streaming messages, uses standard TCP facilities to throttle clients, avoid buffer overflows

• 2014Q1 test reached 2400 nodes as well as starting up a 1000 node cluster in just over four minutes on Google App Engine.

http://akka.io

Who's using it?

Who's using it?

Just about every major player has something in Scala:

• Apple

• Intel

• Twitter

• Agoda

• Airbnb

Who's using it?

Just about every major player has something in Scala:

• Apple

• Intel

• Twitter

• Agoda

• Airbnb

And any company using these scaling technologies:

• Apache Spark

• Apache Scalding

• Apache Kafka

• Twitter Finagle

• Typesafe Akka

Lessons?

• Every developer has the power to enlighten or obfuscate


• Complexity has many different measures at many different levels. The solution of least overall complexity often hides behind greater surface complexity!



• On first glance, Functional Programming looks difficult, but hundreds of years of proven advanced math are what built society – bridges, buildings, cars, computers




• Why reinvent that wheel? Allow mathematical induction to help your efforts.




• Why reinvent that wheel? Allow mathematical induction to help your efforts.

• Moore's Law has given us blessings, including the ability to use increasingly complex compilers.

References + Q&A• Scala Course:

https://www.coursera.org/course/progfun

• Please read chapter 1, available for free: http://manning.com/kuhn/

• Twitter's Scala School:http://twitter.github.io/scala_school/

• Scala Cheat Sheet : http://mbonaci.github.io/scala/

• Deeper insight:http://danielwestheide.com/scala/neophytes.html

https://www.coursera.org/course/progfun

http://manning.com/kuhn/

http://twitter.github.io/scala_school/

http://mbonaci.github.io/scala/

http://danielwestheide.com/scala/neophytes.html

Software Engineering Thailand: Programming with Scala

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