leanovate
Is it dangerous to share references between states?
When transitioning a model using Command.NextState -> commands.State, is it dangerous to share pointers or reference types between model states?
For example,
type State struct {
index map[string]string
}
func (writeFooBarCommand) NextState(s commands.State) commands.State {
current := s.(State)
next := current
next.index["foo"] = "bar"
return next
}
I believe that the existing model state and the new model state will share a reference to the underlying map, meaning manipulations via the old state instance or the new state instance will reflect in both objects. I currently make it a habit to deep copy my model states when transitioning, but my question is whether or not the deep copy is necessary.
In this specific case it should be no problem mutating the state as long as InitialStateGen always generates a new instance.
The main loop running a sequence of commands is done in this function: https://github.com/leanovate/gopter/blob/8de0d746533ed4ca265750b9bcf3ba01839df390/commands/actions.go#L41-L53 As you can see the previous state is just forgotten after the command has been applied, therefore it does not matter if it has been mutated or not.
