Data layer for StepFlow

StateData is the main struct used to store data.

Examples

// create the var/value combination
let email_var = EmailVar::new(VarId::new(0));
let email_val = EmailValue::try_new("test@stepflow.dev").unwrap();

// insert it in a StateData
let mut statedata = StateData::new();
statedata.insert(&email_var.boxed(), email_val.boxed());