DEV Community: liskov

Kotlin Emojis Riddle 😈

liskov — Thu, 25 Mar 2021 16:36:26 +0000

What's wrong with this Kotlin code?

val emojis = listOf(“❤️️“, “🍔”)
val emojiIndex = someNullableInt ?: 0 % (emojis.size - 1)
val selectedEmoji = emojis[emojiIndex]

Let's decompile it to java code:

List emojis = CollectionsKt.listOf(new String[]{“❤️️“, “🍔”})
int emojiIndex = someNullableInt != null ? someNullableInt : 0 % (this.emojis.size() - 1);
String selectedEmoji = (String)this.emojis.get(emojiIndex);

Can you see the problem now?

the answer is below, don't look straight away :)

Answer:

In case someNullableInt is not null, emojiIndex will be assigned with the original value of someNullableInt and not its modulo.
This can cause indexOutOfBoundException.

how can we fix it?

the answer is below, don't look straight away :)

To fix it we need to add () around someNullableInt ?: 0 ->

val emojiIndex = (someNullableInt ?: 0) % (emojis.size - 1)

Which will compile to the following java code:

List emojis = CollectionsKt.listOf(new String[]{“❤️️“, “🍔”})
int emojiIndex = (someNullableInt != null ? someNullableInt : 0) % (this.emojis.size() - 1);
String selectedEmoji = (String)this.emojis.get(emojiIndex);

as you can see, now it will do modulo as expected. Case solved.

Thank you for reading, look for our next Byte

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Cross platform object oriented design 💣💥💥

liskov — Wed, 10 Feb 2021 08:38:42 +0000

Confused about too many names for the same property?

Tired of remembering all names other teams gave to the same feature?

Lisko, please give an example:

A good example from the industry is "String template":

iOS developers call it "String interpolation"
Kotlin developers call it "String template"
Javascript developers call it "Template literals".

But it is the same thing, like this giraffe. The only thing that changes is your point of view.

Shared architecture - same name on every stack

We at Sanga first encounter this issue with our IOS <-> backend
architectures and communications between them. When we saw it work
perfectly and without any misunderstanding we applied it to other sides
of our dev stack such as our frontend sphere, and it fitted like a glove.

The universal design language we created:

Contracts - The objects that pass between our stack parts
View Layer - Controllers, the topmost layer that creates an interface to be consumed (can be UI in an iOS app or REST API in a µservice)
Service - Business logic layer
Repository - Responsible for CRUD operations on our model.
Factory - Responsible for Converting Contracts to Models and vice versa.

Shared code

Shared architecture makes it possible to have a shared code.

We are currently on our journey to find the right way to share code between the different stack layers - but I wouldn't conclude it yet - as we didn't solve this question yet. when we do it will be one hell of a byte!

Thank you for reading, look for our next Byte

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Monorepo

liskov — Wed, 20 Jan 2021 14:43:57 +0000

what?

Monorepo is when putting code of several micro-projects in one code repository.

So it's kind of a Monolith?

Well, that's the missing part of the micro-service architecture.

Splitting our code into micro-projects, each with its own tests, deployment, scaling, etc., introduces a new challenge of maintaining and using many microcode repositories.

Monorepo will hold the collection of micro-project while sharing the echo system of testing, deploying, etc.

when?

When your team needs to run fast -> faster -> fastest.
When there are too many repositories and no one understands what/where they are and if their dependency versions are aligned.
When small library change follows with 30 PR's on 30 git repositories (was the story of my life).
When there are a small number of teams working together because when there are a greater number of teams working on the same git repository, it can do worse than better.

When -> now()

Things to consider while working with a mono repo:

Per micro project build&deploy:
- use git diff to find out what directory changed
- build&deploy only this part
Code owners:
- what team is responsible for what part of the code?
Generate micro project script:
- Creating new microservice should be done in seconds(take a look at https://yeoman.io)
- Each new microservice should be built automatically by the same standard as all other services
Contract lib:
- All services contracts speak in the same language: Rest/Grpc/etc...
- All services use the same libraries with no duplicate code.

Listen to our CTO, Matan Lachmish, talks about Monorepos on Developing Symptoms podcast (for Hebrew speakers)

Thank you for reading, look for our next Byte

Made with ❤️ by Sanga