Xcode has handled this for years. In Xcode, when autocompletion is presented, hitting Tab will complete the longest unique prefixed subword for the currently-selected tab item. If this results in only having one completion option left, then it completes the whole thing (e.g. adding method arguments and whatnot). Similarly, hitting Return will just complete the whole entry instead of the longest unique prefixed subword.
By that I mean if you have 2 autocompletion options `addDefaultFoo()` and `addDefaultBar()`, and you type `add` to get those options, hitting Tab will fill in `addDefault`, and then hitting Tab again will fill in the rest of the selection.
The longest-unique-prefixed-subword is the completion that bash (and tcsh and many other shells) have had for ~30 years now. The non-uniques are listed on the 2nd tab.
By that I mean if you have 2 autocompletion options `addDefaultFoo()` and `addDefaultBar()`, and you type `add` to get those options, hitting Tab will fill in `addDefault`, and then hitting Tab again will fill in the rest of the selection.