Denis Hennessy, Developer in Greystones, Ireland
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Denis Hennessy

Verified Expert  in Engineering

Software Developer

Location
Greystones, Ireland
Toptal Member Since
November 4, 2020

Denis is a passionate engineer who loves building products that people actually use. In particular, he's been building iOS apps since the first iPhone launched. He has a high level of expertise in Swift and Objective-C. Since a modern iOS app is rarely a standalone entity, he's also worked with many external frameworks, including building REST endpoints where SDKs didn't already exist. He's also got experience building large server products, as well as some embedded-systems work.

MacOSLinuxiOSXcodeObjective-CiOS SDKSQLitePostgreSQLSwiftFirebaseRubyPythonSoftware DevelopmentCC++

Availability

Full-time

Preferred Environment

Xcode, MacOS

The most amazing...

...app I've developed is an app that helps people suffering from bipolar disorder to understand their symptoms by recording their mood each day.

Work Experience

Principal Developer

2007 - PRESENT
Peer Assembly
  • Developed a medicine dose tracking app for a pharmaceutical company that provided consumers of the drug an easy to use way to track their usage while providing a significant market advantage for the company.
  • Built a language-learning app for teaching Hebrew to children. I managed all phases of the project from requirements capture, development, testing, and successful launch.
  • Developed a mobile game for a US fast-food chain. Besides being fun to play, the game also was an important part of their customer loyalty program.
Technologies: Objective-C, Swift

Principal iOS Developer

2018 - 2023
Major US Media Company
  • Converted a large portfolio of apps from an ad-supported revenue strategy to a subscription-based offering.
  • Managed a major project evolution from a primarily Objective-C codebase to a primarily Swift codebase, while significantly enhancing the app feature set.
  • Established a continuous-integration system to handle the quality assurance and automated release process.
Technologies: REST, Core Data, Swift, Objective-C

Principal iOS Developer

2016 - 2018
Makalu Inc
  • Took over development of their iOS location bookmarking app, updating it with the latest iOS platform features and adding new photo capabilities.
  • Developed the "event app" for a major annual rock concert under demanding schedule constraints.
  • Developed an educational app which encouraged children to write letters to elected officials.
Technologies: Core Data, Swift, Objective-C

Principal iOS Developer

2014 - 2016
Time Marketing
  • Developed an innovative wine tasting and cataloging app for serious wine enthusiasts.
  • Worked with the project owner and external design freelancer to come up with a unique look and feature set.
  • Managed the evolution of the app from a paid-up-front model to a free-with-IAP model.
Technologies: Core Data, Swift, Objective-C

CTO and Co-founder

1999 - 2007
Valista Inc
  • Handled the architecture of Valista's range of telco-grade payment and messaging products.
  • Managed a distributed development team with centers in Ireland, Sri Lanka, and California.
  • Set up a continuous integration system to improve the quality of software releases and increase the pace of updates.
Technologies: Ruby, Java, C++, C

Lines of Zen

https://linesofzen.com
Lines of Zen is a new kind of meditation app. Instead of trying to empty your mind, you gently focus it by following a series of guided drawing exercises. It's built using Swift and SwiftUI, employing Firebase as a back-end and RevenueCat for subscription management. I was responsible for all development of the project.

Rego - Bookmark Your Places

https://regoapp.com
Rego is an app that lets you easily save "bookmarks" for places you've visited, and attach photos and other data. People use it to save favorite tourist spots, restaurants, and even parking places. The app was originally an upfront payment app and is now free-with-IAP.

Goal Streaks

http://www.goalstreaks.com
Goal Streaks helps you achieve your goals by tracking your daily progress and encouraging you to stick with it for longer and longer streaks. The idea of maintaining a continuous streak is a great motivator to help users stick to a project when they might otherwise quit.

Focus Time

https://focustimeapp.com
Focus Time is an app that helps you practice the Pomodoro Technique—a way of achieving distraction-free work by alternating periods of intense focus, and short breaks to clear your head. I originally wrote the app in 2012.

Languages

Swift, Objective-C, Python, Ruby, C, C++, Java

Frameworks

iOS SDK, SwiftUI, Core Data

Tools

Xcode

Paradigms

REST

Platforms

MacOS, Linux, iOS, Firebase

Storage

SQLite, PostgreSQL, Cloud Firestore

Other

Software Development

Collaboration That Works

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