Note that std::future references shared state that is not shared with any other asynchronous return objects (as opposed to std::shared_future).
The code above might look ugly, but all you have to understand is that the FutureBuilder widget takes two arguments: future and builder, future is just the future you want to use, while builder is a function that takes two parameters and returns a widget. FutureBuilder will run this function before and after the future completes.
A std::futureA future statement is a directive to the compiler that a particular module should be compiled using syntax or semantics that will be available in a specified future release of Python. The future statement is intended to ease migration to future versions of Python that introduce incompatible changes to the language. It allows use of the new features on a per-module basis before the release in ...
What is future in Python used for and how/when to use it, and how ...
If that expression is invalid, the behavior is undefined. Any value returned from the continuation is stored as the result in the shared state of the returned future object. Any exception propagated from the execution of the continuation is stored as the exceptional result in the shared state of the returned future object.