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articles/2026-02_KMP-en.md

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+TODO-Title: Does LinkedIn publication have a title?
+TODO-URL: LinkedIn
+TODO: Вернуть хостинг своего сайта на GitHub?
+TODO: Починить открытие видеозаписей
+TODO: Сделать ссылку на Русскую статью из Английской
+TODO: Сделать ссылку из Английской статьи на Русскую
+
+Is Kotlin Multiplatform able to cut development costs for products
+that support multiple platforms? My calculations say yes, by 21%.
+
+# Current state of products for multiple platforms
+
+One of the most popular ways to develop for multiple platforms relies on having
+a separate team for each platform. For example, here's one particular bug I faced
+in the russian messenger MAX some time ago:
+
+<iframe src="https://kornerr.ru/vid/max-msg-disappear_2026-01-28.mp4"></iframe>
+
+As you can see, while I was chatting with GigaChat AI my messages were
+disappearing: Android had the bug once (the 4th second), Web had
+the bug multiple times. Having a different behavior on multiple platforms means
+there are different teams doing the same product for multiple platforms. Each
+team has its own programming language, its own architecture, its own code review
+process, its own set of unique bugs, its own team of testers, its own wage fund,
+and so on.
+
+Thus, the more we duplicate the code, the more we have to duplicate the
+organization structures. Kotlin Multiplatform (KMP) can help reduce code
+duplication. Of course, KMP won't remove code duplication completely, only
+to some degree. Let's have a look at my hobby project GitBudget to find out
+that degree.
+
+# GitBudget summary
+
+GitBudget is a tiny hobby project to help me ease calculating my day-to-day
+spendings. Currently there's no history, no Git support, etc. Nonetheless
+I've been using it for several months now to speed up tedious calculations of
+the two important figures:
+
+1. Overrun: Did I spend more than my daily budget allows? If so, how many rubles?
+2. Left ₽/day: How many more rubles do I have left to spend a day by taking the overrun into account?
+
+I don't intend to dive deep into the formulas, it's outside the topic of the article.
+If you're interested you can have a look at the source code here
+[at GitHub](https://github.com/kornerr/git-budget).
+
+Let's see how the application looks like for Android and iOS:
+
+![Android, iOS](https://habrastorage.org/webt/e2/bz/f5/e2bzf5lblg0xsydakc88zb5a_hu.jpeg)
+
+No fancy UI/UX here, each UI element is a standard one (sometimes not even
+aligned correctly). As a user I usually use the application the following way:
+
+1. Paste from the clipboard the sum I spent yesterday (Spent)
+2. Paste from the clipboard the remaining budget balance I had for yesterday's morning (Morning balance)
+3. Copy the result of calculations into the clipboard (Result)
+
+# Development costs
+
+Let's divide the source code by three groups;
+
+| № | Group | Example | Android files | iOS files |
+| --- | --- | --- | --- | --- |
+| 1 | UI | Jetpack Compose, SwiftUI | MainActivity.kt, VM.kt | AppView.swift, VM.swift |
+| 2 | Platform | ClipboardManager, UIPasteboard | budget.kt, main.kt, other-android.kt, registerOneliners.kt | budget.swift, cld-ios.swift, other-ios.swift |
+| 3 | Logic | budgetShouldResetMorningBalance | budgetFun.kt, entities.yml | budgetFun.kt, entities.yml |
+
+I use KMP only for logic in GitBudget. UI and platform code are native. Why?
+Because logic is under my full control, it's only updated when I need it.
+UI and platform, on the other hand, are the properties of Apple and Google.
+They dictate the rules and update UI with the platform to their liking
+(for instance, Apple's unavoidable [Liquid Glass](https://www.nngroup.com/articles/liquid-glass/)).
+
+We'll have a look at two objective indicators: lines of code and time spent to
+implement a functionality.
+
+## Indicator #1: Lines of code
+
+| № | OS | Total | UI | Platform | Logic |
+| --- | --- | --- | --- | --- | --- |
+| 1 | Android | 692 | 160 (23%) | 221 (32%) | 311 (45%) |
+| 2 | iOS | 540 | 90 (16%) | 139 (26%) | 311 (58%) |
+
+**Conclusion-1**: I didn't write 311 lines of code for iOS **again** thanks to KMP, that's **58%** of all iOS code
+
+**Conclusion-2**: From the perspective of both operating systems (692 + 540 = 1232), these 311 unwritten iOS lines of code result in **25%** of code I didn't write for the whole project
+
+## Indicator #2: Time spent to implement a functionality
+
+I've recorded the process of adding a new `Paste` button for `Morning balance` input both for Android:
+<iframe src="https://kornerr.ru/vid/git-budget-balance-android_800_2026-01-28.mp4"></iframe>
+
+And iOS:
+<iframe src="https://kornerr.ru/vid/git-budget-balance-ios_800_2026-01-28.mp4"></iframe>
+
+The results are:
+
+| № | OS | Implementation type | Description | Time |
+| --- | --- | --- | --- | --- |
+| 1 | Android | Initial | I've created a new functionality that has not existed before | 17:34 |
+| 2 | iOS | Secondary | I've used already existing logic in KMP, only added a new UI | 07:33 (43%) |
+
+**Conclusion-3**: It took **57%** less time to repeat the functionality for iOS, i.e., it happened **2 times faster**
+
+**Conclusion-4**: If we assume that creating the same functionality for both OSes without KMP would take 17:34 * 2 = 35 minutes, then the saved 10 minutes to repeat the functionality for iOS result in **21% of saved time** for the whole project
+
+# Conclusions
+
+Thus, these are the figures when using KMP:
+
+1. iOS lines of code down by **58%**
+2. Total project's lines of code down by **25%**
+3. Time spent to repeat the functionality for iOS down by **57%**
+4. Total time spent to implement the functionality for the project as a whole down by **21%** (this is the figure I've used in the beginning of the article)
+
+# Questions to a reader
+
+1. Is 21% of saved time worth it?
+2. Is 21% good enough to actually step into KMP realm yourself?
+3. How important is it to synchronously release the same functionality for both OSes?
+