Option
Optional values are specified using the type Option t, where t is some type. The Option ADT has two constructors:
Some represents the presence of a value. The Some constructor takes one argument (the value, of type t).
None represents the absence of a value. The None constructor takes no arguments.
Example contract#
scilla_version 0(************************************************************************)(* Scilla's Option type: a type that either is "empty" ("None") or has *)(* a Uint32 ("Some {Uint32}") *)(* How to i) create (with and without value), (ii) to extract the value *)(* and iii) do different things depending if the Option is empty or not *)(************************************************************************)library Option
let empty_option = None {Uint32}
contract Option()
(* mutable fields declarations *)field opt : Option Uint32 = empty_option
(* give the option a value *)transition SetTo(v: Uint32) o = Some {Uint32} v; opt := oend
(* remove the value in the option *)transition Clear() o = empty_option; opt := oend
(* extract the value (if any) and emit *)transition Emit() o <- opt; match o with (* depending on Option state, do different things *) | None => ev = {_eventname: "EmitNone"}; event ev | Some v => ev = {_eventname: "EmitValue"; value: v}; event ev endend