[JAVA] I went to Scala Fukuoka 2019!

I participated in ** Scala Fukuoka 2019 ** held at LINE Fukuoka on January 19, 2019!

2019/01/19 (Sat) 11: 00- LINE Fukuoka https://scala-fukuoka.org

opening

• There are quite a lot of first-time participants.
• There are many participants from outside Kyushu.
• There are still few Scala engineers in Fukuoka, but there were many applications for CfP.

Keynote-When to use Scala and when not to use it

Gakuzo-san (Tech to Value) @gakuzzzz

A summary of Scala's language characteristics and surrounding environment, and Scala's orientation.

Scala language characteristics

• Statically typed language.

• For critical applications, statically typed languages are better suited.

• Dynamically typed language is an idea to avoid a state where the whole does not work even if there is a problem in a part.

• The expressive power of types is higher than that of Java.

• Also suitable for Domain Driven Design (DDD).

• Metaprogramming (reflection, macros, etc.) is as easy as Java.

• Scala macros are still experimental features and are likely to change in the future.

• The paradigm is object-oriented and functional integration.

• Subtyping is Nominal Subtyping.

• Besides, Go is Structual Subtyping and Ruby is Duck Typing.

• Suitable for products that are subject to continuous changes. If it's left unchanged, it might be too much.

Library circumstances

• JavaScript is the overwhelming number of repositories on GitHub. There is also a lot of Java. Scala and Go are still few.

• Scala products include Spark and Akka.

• In many cases, Scala is selected to use Akka.

• The advantage of Scala is that you can use the Java library as it is.

• However, many libraries for Java are designed to be mutable, and it may be a little difficult to use from Scala, which is based on immutables.

Around the runtime

• Scala runs on the JVM.
• Among statically typed functional languages, it is advantageous to be able to use the dead runtime and abundant profiling tools.
• The weight of JVM startup can be a disadvantage. (Cloud services like AWS Lambada)

community

• There are few Scala engineers.

• It is said that the learning cost of Scala is high, but in reality it is not due to language characteristics, but it may be due to other factors.

• In the first place, it is very difficult to program properly in an object-oriented manner.

• Note: Many engineers are giving up and switching to functional programming.

Practice Clean Architecture

Mr. Fujii (chat work) @yoshiyoshifujii

An explanation of the points of clean architecture and an introduction of implementation examples in Scala.

https://speakerdeck.com/yoshiyoshifujii/shi-jian-clean-architecture

Separation of policy and details

• Policy: Product value and purpose.

• Details: Means of product realization. Frameworks and middleware.

• The purpose is to separate the heart.

• I want to focus on "policy".

• I'm addicted to DDD.

• I want the "policy" not to depend on the "details".

• To consider "details", implement "policy".

SOLID principle

• Single responsibility principle.
• Open / closed principle.
• Liskov Substitution Principle.
• Principle of interface separation
• Dependency inversion principle.
• Business rules can be made independent by the principle of dependency reversal.

Component principles

• Principle of reuse / release equivalence.
• Common principle of closure.
• Principle of total reuse.

There are conflicting points, so balance is important.

Clean architecture

• Put a "policy" at the center.
• Depends on the center (policy) from the outside (details).
• When combined with DDD, the domain model applies to Entities.

Practice in Scala

See slide.

Sponsor Lunch Session A

nulab

• backlog and typetalk use Scala (Play Framework).
• Nulab Apps uses Java / Kotlin (Spring Framework).
• There are many in-house systems that use Scala.

Sponsor Lunch Session B

forkwel

• 297 community sponsors over 10 million yen

• Know your ideals and know the gap with reality.

• The average annual income of Scala engineers is number one. However, there is not much difference in income between languages.

• If you want to make more money, it's quicker to join a profitable company than to differentiate your skills.

• Turn the loop of outputting and receiving feedback.

• It is important to verbalize.

• Learn bargaining skills.

• Market evaluation> In-house evaluation ・ ・ ・ I cannot get a fair reward.

• Market evaluation <In-house evaluation ・ ・ ・ Not crushable

• Market evaluation = In-house evaluation ・ ・ ・ Ideal.

• By appealing both inside and outside the company and balancing the evaluations, you will be able to work freely.

Domain modeling with Scala code

Jun Kato (chat work) @ j5ik2o

Introducing the domain modeling method focusing on domain events and the implementation example by Scala.

https://speakerdeck.com/j5ik2o/scalakodototomonikao-erudomeinmoderingu

Modeling with domain events

Use Case

• Important business rules lurking in the rainy day course (exception case).
• Discuss business rules while writing a use case description.

People, things, things

• Human: Actor outside the system

• Things ... Domain model

• Things ... Domain event

• Since things represent the relationship between people and things, we will focus on things and organize things.

• Event Storming

• Use cases-> Domain events-> Commands (operations)-> Actors and domain models

Modeling flow

• A domain event is a concern expressed in the past.
• Check if the identified domain events are arranged in chronological order and if there are any omissions.
• If you can identify the domain event, you can also know the command that triggers it.
• Update the lead model to the latest state in response to the domain event. (CQRS pattern)
• Execute the command and think about which domain model is responsible for issuing domain events.

Implementation by Event Sourcing

• The domain model (aggregate route) has a history (list) of domain events.

• The domain model is set to trait so that the model does not depend on the means of implementation (Event Soucing).

• Business methods generate a new domain event and add it to the end of its event column and return it.

• If multiple business methods must be called as a set, there is a way to implement it as a domain service.

• Keep business methods invisible from the outside.

• In the repository, insert the event column.

• It is necessary to prevent the order of event columns from being out of order (locking, etc.) when trying to persist from multiple threads and multiple processes at the same time.

• With Akka Cluster, there is always one actor with an instance of the aggregate route, so there is no conflict.

Consistency across aggregates

• Eventual consistency is better.
• Generating the entity ID will be difficult if it is automatically numbered at the time of persistence, so it should be numbered programmatically in advance.
• FK is not compatible with eventual consistency.

Beginning with Databricks and Spark [Big Data ETL Processing / Data Visualization] Introduction to Practice

Mr. Shimada (Every) @smdmts

Explanation of databricks / Spark practice and data visualization. (I don't have much prior knowledge of data analysis, so I can't keep up with it ...)

https://speakerdeck.com/smdmts/databricks-and-spark-with-etl-and-visualization

Databricks

• Spark-based data analysis platform.
• Spark cluster scaling.
• Notebook: A function that allows you to execute Spark processing while checking with Step by Step. Write code in Scala / Python / SQL etc.

ETL

• Extract ・ ・ ・ Data extraction
• Transform ・ ・ ・ Data type conversion
• Load ・ ・ ・ Persistence

As a result of trying Scala with Sier, the story of changing jobs to the Web system

Mr. Hosoya (CyberAgent) @bake_nezumi

https://www.slideshare.net/bakenezumi/sierscala-web

The story of introducing Scala with SIer.

• Play Framework can be used in both Scala / Java.

• Java assets can be reused.

• Language features such as pattern matching and immutable programming.

• Note: Using Java O / R mapper from Scala seems painful.

• Doma wrapper for Scala https://github.com/bakenezumi/domala

How to Learn New Programming Languages ~ Scala Learned with Parza Combinator Library ~

Mr. Mizushima (Dwango) @kmizu

http://kmizu.github.io/scalafukuoka2019/#/

You have already mastered one or more programming languages, and how to learn a new programming language.

• Barriers to learning other languages.

• There is an opinion that if you understand one language, you can understand another language.

• It is difficult to learn an unknown paradigm.

• It is important to understand the structure common to many languages.

syntax

Concrete syntax

• Generally referred to as "syntax". How to write an if statement.
• Can be strictly defined by BNF.
• It only expresses the appearance (writing style) of the syntax, and includes non-essential things (such as parentheses and spaces).

Abstract syntax

• The concrete syntax with information unnecessary for interpreting the program removed.
• It is important to understand the abstract syntax.

Type system

Derived type (subtyping)

• Name partial type: General subtyping. Substitution is possible only when there is an inheritance relationship.
• Structural partial type: Static duck typing. Substitution is possible as long as you have the required method even if there is no inheritance relationship.

Polymorphic type (generics)

• Whether type parameters can be used.

Semantics

• A definition of how a program is executed.
• It can be said that it defines how to convert the abstract syntax tree.

How to learn a language

• It is better to break it down into the above syntax, type system, and semantics.

• What kind of program should I write to learn? → A parser combinator is suitable.

• Because you will use various functions of the language, you can understand the main points of the language.

• Have your own "Hello World".

LT

Emotional Scala

@HonMarkHunt (Bizreach)

• Scala history 4 months.
• Hashtag # Emosca
• "Scala logo ww"

Write \ / and read as disjunction

Daigoro-san (Rakuten)

• Scalaz should be used from a place that is easy to understand.

Quick introduction to scalafix

Mr. Taniguchi (Hatena) @tanishiking

https://speakerdeck.com/tanishiking/quick-introduction-to-scalafix

• Scalafix ・ ・ ・ Refactoring and linting tool for Scala
• Scala.meta (a library for parsing Scala programs) is used.

Apache Kafka

Mushrooms (freelance) @ aa7th

https://speakerdeck.com/sammy7th/apachekafkanituitetiyotutomian-qiang-simasita

• Apache Kafka ・ ・ ・ Messaging middleware.
• Handwritten presentation on iPad Pro.

Run Scala on GraalVM

Kishida-san (LINE) @kis

http://d.hatena.ne.jp/nowokay/20190120#1548011826

• Graal ・ ・ ・ JIT compilation written in Java.
• The GraalVM compiler compiles Java bytecode into native code.

1. Make FAT-jar with sbt assembly.
2. Natively compile with native-image -jar ****. Jar on GraalVM.

• Why do you want to be native?

• Starts up faster. (However, Scala Native is a little faster)

• All Java libraries can be used. (Scala Native can only use the provided libraries)

• There are pitfalls such as a natively compiled tail-optimized program but an error at runtime.

Digression

We got on the front in Fukuoka and started out on the night of Hakata with four engineers who are getting along well.

The offal grilled shop here is already exquisite, and I thought I would like to go there again when I come to Hakata.