State of a function call after yielding.
Calling @GDScript.yield within a function will cause that function to yield and return its current state as an object of this type. The yielded function call can then be resumed later by calling resume on this state object.
Check whether the function call may be resumed. This is not the case if the function state was already resumed.
extended_check is enabled, it also checks if the associated script and object still exist. The extended check is done in debug mode as part of GDScriptFunctionState.resume, but you can use this if you know you may be trying to resume without knowing for sure the object and/or script have survived up to that point.
Resume execution of the yielded function call.
This function returns what the resumed function call returns, possibly another function state if yielded again.