The way to answer your two questions is to combine them, the definition of “a while” depends on how good a job the interface does. If the interface is really go

The way to answer your two questions is to combine them, the definition of “a while” depends on how good a job the interface does. If the interface is really good, then it can last a really long time (perhaps as long as the language lasts). I read some discussion the other day about some ways in which the Any type in Rust isn’t as flexible as it could be, since it is frozen the only way to improve it would be to introduce a new name, such as Unknown. Similarly in C# along with adding async support, the standard library added async versions of many methods, eg Read now also has a ReadAsync partner. It does seem that having multiple names for basically the same thing adds a small but tolerable level of overhead to a language. At least if as much as possible is moved out, then projects can choose to only use the latest versions, and live in a world as if past versions never existed.