I mean things like containers though in the context of a new language chances are the language itself may provide functionality that makes moc unnecessary.

Also you certainly do not need something like moc to make a GUI library, which comes back to what i originally wrote in that you do not need to replicate Qt to have a GUI library.

"containers" was not in the list.

There sure is some overlap with what Qt offers that most language offers (Containers, Networking, Database, threading, ...). But purely in the context of making a UI library, there is still a huge amount of things that Qt offers that needs to be replicated.

The post i replied to was about how big Qt is, which includes containers, etc. That the specific examples given did not contain "containers" isn't relevant since they are part of the "2 million LOC" mentioned.

Yes, you need to implement similar functionality, like abstracting the window system, input handling, text, etc but you do not need to replicate what Qt does to have a GUI toolkit.

Qt is very complex and Qt is (among others) a GUI library but Qt being complex doesn't mean that GUI libraries have to be complex.

...but, as others have noted, even if you want to only support the "core" features that most people would take for granted for a GUI (cross-platform, all the "usual" widgets including complicated ones such as RichEdit, ListView, TreeView, text with Unicode support and subpixel rendering etc. etc.) it's already a massive undertaking.

That is another issue, yes, it is not trivial (though it isn't like making a browser or even a game engine - especially since game engines nowadays tend to have their own GUI toolkits :-P) but my point was that you do not need to replicate what Qt does to have a useful and usable library.