Title here
Summary here
Enums in Fortran
Our enum type ServerState has an underlying integer type.
MODULE ServerModule
IMPLICIT NONE
INTEGER, PARAMETER :: StateIdle = 0
INTEGER, PARAMETER :: StateConnected = 1
INTEGER, PARAMETER :: StateError = 2
INTEGER, PARAMETER :: StateRetrying = 3
CONTAINS
FUNCTION StateToString(state) RESULT(stateStr)
IMPLICIT NONE
INTEGER, INTENT(IN) :: state
CHARACTER(LEN=10) :: stateStr
SELECT CASE (state)
CASE (StateIdle)
stateStr = "idle"
CASE (StateConnected)
stateStr = "connected"
CASE (StateError)
stateStr = "error"
CASE (StateRetrying)
stateStr = "retrying"
CASE DEFAULT
stateStr = "unknown"
END SELECT
END FUNCTION StateToString
FUNCTION Transition(state) RESULT(newState)
IMPLICIT NONE
INTEGER, INTENT(IN) :: state
INTEGER :: newState
SELECT CASE (state)
CASE (StateIdle)
newState = StateConnected
CASE (StateConnected, StateRetrying)
newState = StateIdle
CASE (StateError)
newState = StateError
CASE DEFAULT
PRINT *, "Error: unknown state"
STOP
END SELECT
END FUNCTION Transition
END MODULE ServerModuleTo use the ServerState type and demonstrate state transitions, we can create a simple program:
PROGRAM TestServerState
USE ServerModule
IMPLICIT NONE
INTEGER :: ns, ns2
ns = Transition(StateIdle)
PRINT *, StateToString(ns)
ns2 = Transition(ns)
PRINT *, StateToString(ns2)
END PROGRAM TestServerStateWhen running the program, it will emulate a state transition for a server and prints the state in string format:
$ gfortran -o server_test ServerModule.f90 TestServerState.f90
$ ./server_test
connected
idleBy implementing the StateToString function and using a SELECT CASE construct, we ensure a similar behavior to enums in languages with native enum support. The Transition function handles state transitions safely, mimicking some level of type safety.