Until very recently, Dropbox had a technical strategy on mobile of sharing code between iOS and Android via C++. The idea behind this strategy was simple—write the code once in C++ instead of twice in Java and Objective C. We adopted this C++ strategy back in 2013, when our mobile engineering team was relatively small and needed to support a fast growing mobile roadmap. We needed to find a way to leverage this small team to quickly ship lots of code on both Android and iOS. We have now completely backed off from this strategy in favor of using each platforms’ native languages (primarily Swift and Kotlin, which didn’t exist when we started out). This decision was due to the (not so) hidden cost associated with code sharing. Here are some of the things we learned as a company on what it costs to effectively share code. And they all stem from the same basic issue: By writing code in a non-standard fashion, we took on overhead that we would have not had to worry about had we stayed with the widely used platform defaults. This overhead ended up being more expensive than just writing the code twice.