Coupang PlaySenior iOS Developer · Sports Squad
2023.07–2026.04New sports calendar, Discover feed revamp, live-status package design, code modernization
Jaemyeong Jin
iOS Software Engineer
About
Apple platform engineer who has built iOS apps at Coupang Play, Goodoc, and Sendy. At a large-scale OTT service, I built the sports calendar and match details from scratch and developed sports screens for iPhone, iPad, and Apple TV; at startups, I owned apps from design to release as the sole iOS developer. I enjoy gaining insight by trying new technologies hands-on, and recently I have been learning Rust, RAG, local LLMs, and AI agents through personal PoC projects and applying them to improve development productivity.
Core Competencies
- Fundamentals: Worked with everything from pre-ARC Objective-C (manual retain/release) to Swift Concurrency; experienced in managing view controller and Task lifecycles in mixed UIKit/SwiftUI screens.
- Problem solving: Reproduced symptoms and narrowed down root causes with Instruments and Xcode debugging tools to fix memory leaks, unnecessary view rebuilds, and race conditions.
- Collaboration: Built and shipped features in a squad that brought PM, design, backend, and QA into one team; shared packages I designed were also used in other developers' features.
- Testing: Extract async state logic into SPM packages verified by about 60 Swift Testing unit tests, and deliberately inject defects to confirm the tests fail.
AI Competencies
- AI agent–based development: After problem definition and research, I first set the scope of changes and completion criteria with a spec and plan, then build a harness that keeps agents within them. I split implementation and review across different agents (Codex, Claude) for cross-verification, and run the full test suite myself to confirm.
- AI product development: In a nutrition analysis PoC, prevented hallucination with a RAG architecture that uses only values from retrieved source data; in a local LLM environment, studied model architecture and quantization and served a quantized model myself.
Tech Stack
Swift · Objective-C · UIKit · SwiftUI · Swift Concurrency · Combine · RxSwift · Swift Testing · XCTest · SPM · Xcode Cloud · GitHub Actions · TypeScript · React Native
Key Experience
GoodocFrontend Developer · Core Team iOS
2022.05–2023.07Hospital booking and check-in, iOS app maintainer, App Store ownership transfer
SendyLead iOS Developer
2020.08–2022.03Sole iOS developer: app design and launch, payments, Combine migration, CI/release automation
FavorieDeveloper
2016.12–2020.04Video, healthcare, and scheduling iOS apps; Objective-C to Swift migration
Experience
Coupang Corp.Senior iOS Developer · Sports Squad
2023.07–2026.04 · Coupang Play for iOS, iPadOS, and tvOS
Coupang Play is a large-scale OTT service offering movies, dramas, and live sports. In the Sports Squad, I was responsible for the screens from browsing matches to entering live streams. The squad brought PM, design, backend, QA, and frontend (web and mobile) together in one team to build features, and I also worked with engineers in Korea and abroad and with external partners to ship features on fixed schedules.
New Features
- New sports calendar and match details: Built new screens that let viewers find matches by date and league and go into the live stream. SwiftUI bidirectional infinite-scroll date picker, match list, league filter, and loading, empty, and error states.
- Discover feed sports revamp: Added SwiftUI Hero, live rail, and Top10 sections to the Diffable Data Source–based feed, with iPad support.
- League standings and match lineups: Spreadsheet-style Compositional Layout combining fixed columns with horizontally scrolling stat columns.
- tvOS and live chat: Sports Pass subscription pop-up, 4K/HDR badges, live dot animation, report/block bottom sheet with custom presentation transitions.
Technical Deep Dives
These were not assigned tasks; I found them during development, traced their causes, and fixed them.
- Child view controller leak in SwiftUI hosting cells: With UIHostingController placed inside UICollectionView cells, the previous UIHostingController remained a child of the parent view controller when a cell was reused. Fixed by detaching both the view and the child controller in prepareForReuse.
- Live rail flicker: Every status update for the same match, delivered on a 1-second cycle, reset the model and rebuilt the section. Eliminated by keeping the model when the match identifier is unchanged and updating only the content of visible cells.
- Tab-switch race condition: After rapid tab switching, a late-arriving response was applied to the current tab's Hero. Blocked by checking the current tab context at display time.
Shared Foundations and Code Modernization
- Designed two SPM packages for live-status observation: Packages that let multiple screens observe changes in a match's live status. Designed on actor, AsyncThrowingStream, and Sendable, and verified by about 60 Swift Testing unit tests. Also used in other developers' features.
- Observation Task lifecycle management: Tied Task start and cancellation to when a screen appears, disappears, and is deallocated.
- Network layer modernization: Wrote 16 URLSession request types, migrated legacy APIs, and expanded the use of async/await.
- Screen architecture modernization: Removed the IGListKit dependency from 5 areas.
- Legacy library migration to SPM: Proposed and carried out moving legacy libraries, which were embedded in the repository as source and binaries, into SPM packages.
- Use of AI tools: Used company-approved AI models to investigate bug causes, find code related to requirements documents, and fix simple bugs.
GoodocFrontend Developer · Core Team iOS
2022.05–2023.07 · Goodoc, a hospital booking and check-in service
- Booking and check-in features: Developed hospital booking and mobile check-in, a booking date calendar, forms, and an operations back office. About 80,000 bookings processed in the 6 months after launch. (TypeScript, React, React Native)
- iOS app maintainer: Organized native modules and project conventions, handled App Store releases and incident response, and took part in a full redesign of the main home tab.
- App Store app ownership transfer: Ran the process in direct communication with Apple and reviewed user impact in advance.
- Booking notification links: Implemented the flow that goes through login and list loading to the target booking's detail screen.
SendyLead iOS Developer
2020.08–2022.03 · Sendy, a truck and freight delivery ordering service, and Isamoa, a moving service
- Sendy iOS app design, development, and release: Designed the app from scratch and shipped it as the sole iOS developer. MVVM-C architecture; Naver Pay, Kakao Pay, and NICEPAY payment integration.
- Payment reliability: In WKWebView payments, re-fetched the order details before routing to the result screen instead of judging completion from external app callbacks alone.
- Design system and modularization: Built a design system of color, typography, and spacing tokens and shared UI components together with the designer, and modularized the app into local SPM packages. Proposed and led both efforts.
- Code and release modernization: Migrated from RxSwift to Combine, set up CI and release automation on GitHub Actions and Xcode Cloud, and tested the auth refresh API. (XCTest)
- Isamoa: Took over an undocumented legacy app, understood it through code analysis, consolidated it around Swift, and moved it from MVC to MVVM. Replaced the address search API and added iOS 15 support.
FavorieDeveloper
2016.12–2020.04 · Healthcare, scheduling, and video iOS apps and web services
- Cliplog (video filter app): AVFoundation camera control and video recording, Core Image filters, MVVM design.
- Vivace (healthcare app): Step tracking with HealthKit and Core Motion; migrated from Objective-C to Swift. Handled the edge case where the weekly activity report could not compute the rate of change when the previous week's activity was 0.
- AT (scheduling app): Migrated from Objective-C to Swift (setting up AppDelegate and the bridge), Today Extension widget, iCloud sync and backup.
- Pathfinder: Vue/Nuxt website and admin system, Apollo GraphQL, CircleCI and AWS ECS deployment.
Education, Military Service, Certifications & Awards
- B.S. in Computer Engineering, Kyungsung University2007.03–2014.02
- Republic of Korea Army, Sergeant, honorably discharged after completing service2014.11–2016.08
- Engineer Information Processing2012.06
- First Prize, 5th Bu:Star Challenge Game Contest2020.11
- First Prize, 1st Busan Mobile App Contest · iPhone app2011.01