"Flutter, offering high performance and energy efficiency for SNCF Connect"

New design, new features and new app: the launch of the SNCF Connect website and app made a big bang in 2022. One of the secrets of its design? Many technical innovations have been incorporated into SNCF Connect, with state-of-the-art solutions. One of the key technical choices made by the SNCF Connect & Tech teams was to bank on the Flutter framework, still in its infancy at the time, to build everything faster and better. François Nollen, Staff Engineer at SNCF Connect & Tech, provides an insight into this project.

Can you introduce yourself and tell us about your role at SNCF Connect & Tech?

I joined SNCF Connect & Tech in 2013 where I'm now a staff engineer. I work with all the tech teams on a wide range of subjects, including architecture choices, specific expertise, methods and tools. I also help developers share their experience with the community. My day-to-day work involves a lot of coordination with all the teams in the company: discussing code, monitoring, sharing practices... Basically, everything that contributes to helping the teams in their roles – including taking on board innovative technologies like Flutter!

Why did you choose Flutter to develop SNCF Connect?

Late 2020, our ambition was to build the entire SNCF Connect app 'from scratch' in just one year. We tested several 'cross-platform' solutions to speed up development while improving the quality of the app for users. In our tests, Flutter came out on top against React Native and Kotlin Multiplatform, thanks to its performance, rapid learning curve, tool quality and very dynamic community. It was a bold gamble given that Flutter was still a young technology, but it lived up to all its promises! The teams adopted it very quickly, a large part of the mobile code was factorised, the feedback from the teams was very good... and above all, the product was delivered on time!

What do you mean by the 'code was factorised'?

It's very simple. Before, to offer an iOS app and an Android app, or for a new feature, we had to write the code twice in two different languages. We had several dedicated teams, and it required more effort and synchronisation to launch a feature at the same time on two platforms. With Flutter, 90% of our mobile code is mutualised: we write a single code that works for both platforms – write once, run everywhere. We're faster and make fewer errors. Even after the launch of SNCF Connect, this has enabled us to offer new features to users every week. By producing and maintaining less code, we not only save time, we also save resources, deploying less effort, less testing and less infrastructure while gaining more efficiency to create value.

How does Flutter fit into your processes today?

Flutter has become a central app base for our teams. On SNCF Connect, it allows more features to be rolled out quickly, with high performance for users and a consistent experience between iOS and Android. With around 150 screens in total, SNCF Connect is one of the biggest Flutter apps in Europe. And the framework is constantly evolving and being extended to other platforms. For the past two years, our teams have also been using other facets of the framework, such as Flutter Web, to build internal tools and other business line projects.

What are the tangible benefits for your teams and users?

The benefits are particularly visible for our teams. Flutter has won over even the most experienced team members and those most attached to a particular platform. What's more, Flutter has also appealed to some back-end developers who have chosen to switch to mobile development! It's a modern, high-performance, open-source framework with a welcoming and very active community. The support of the Google teams and the entire Flutter community has been a key asset in creating SNCF Connect and continuing to innovate and enrich the app since its launch. In fact, our teams have made a habit of taking part in community events and sharing feedback, discoveries and even code created in-house at meetups, international conferences and via articles published on our technical blog, so that innovation is accessible to all.

For users, even if they don't know what's going on under the bonnet, the benefits are twofold: more features, very regular updates, and a streamlined, high-performance experience on as many devices as possible, plus an increasingly energy-efficient app. We're actively working on this aspect, optimising the app for older or less powerful devices, or in special conditions (low battery, unstable network). For example, we can reduce animation, geolocation accuracy and more. By adjusting the right parameters for each device, we can both limit consumption and improve the user experience.

Is this 'low tech' approach set to grow?

It should! Digital technology has an environmental footprint, especially mobile devices, which are expensive to produce and are replaced too often. Flutter allows us to develop more features with less code. To take things a step further, we're trying to reduce the consumption of apps on user devices. We firmly believe that this approach has a future in improving the experience and consumption of apps, and not just SNCF Connect. On a large scale, even simple optimisations can have an impact. That's why we've created a Flutter Eco Mode plugin that we share as open source with the Flutter community. Sharing code and making innovation accessible to all are also a good way forward.