For simplicity, allow typestates on enums, booleans and optional types only?


type T = private [typestate state (Uninitialized, Connected, Closed)]

type T = (
    # storing the typestate here is optional, unless there are functions that have typestates in "when" clauses
    enum (Uninitialized, Connected, Closed) state
    int socket [state in Connected]
    int bytes_written [state in Connected,Closed]
)

func create_socket()
returns rwref takeown T [return.state to Uninitialied]

func connect(rwref T this, ref SockAddr addr, int port)
returns |neterror.noroute [T.state from Uninitialized, when success(return) T.state to Connected]



---
alt. syntax:


func create_socket()
returns rwref takeown T
typestate return.state to Uninitialied

func connect(rwref T this, ref SockAddr addr, int port)
returns |neterror.noroute
typestate T.state from Uninitialized
typestate T.state to Connected when success(return)
# ^ if there is only one typestate it should be enough to say "typestate T to/from ..."

# example of wildcard typestate usage
func connect(rwref T this, ref SockAddr addr, int port)
returns |neterror.noroute
typestate T.state to Connected when T.state from Uninitialized and success(return)



---
alt syntax 2:


func create_socket()
returns rwref takeown T
postcond typestate return.state == Uninitialied

func connect(rwref T this, ref SockAddr addr, int port)
returns |neterror.noroute
precond typestate T.state == Uninitialized
postcond typestate T.state == Connected when success(return)
# ^ if there is only one typestate it should be enough to say "typestate T to/from ..."

# example of wildcard typestate usage
func connect(rwref T this, ref SockAddr addr, int port)
returns |neterror.noroute
typestate T.state to Connected when T.state from Uninitialized and success(return)