Generally, namespaces are open so it is perfectly legal to expand existing namespaces with additional declarations and definitions in several files. The only exception to the rule is namespace std. According to the C++ Standard, the result of modifying namespace std with additional declarations–let alone a removal of existing ones–is undefined and should be avoided. This restriction may seem arbitrary but it’s just common sense; any attempt to tamper with namespace std undermines the very concept of a namespace dedicated exclusively to standard declarations.
When it launched in 2008, the Apple App Store only had 500 apps available. By the first quarter of 2022, the store had about 2.18 million iOS-exclusive apps. Average monthly app releases for the platform reached 34,000 in the first half of 2022, indicating rapid growth in iOS app development.