Return

Return(); is equivalent to Return(Invalid);

Use in Launched Modules / Subroutines

If a Return statement appears anywhere in the code of a launched module (i.e. one that is executed inside of a script or using the Launch statement), even if that portion of the code is not executed, the module will be considered to be a called module, and will block execution of all other modules in the same thread while it is executing.

Execution of the Return statement in a subroutine results in the module being slain without having to use the Slay statement.

Use in Called Modules

If the Return statement is used in a called module (one that appears as a statement in a state), execution of the Return statement will not stop the execution of the calling module.

The return value for the module is set equal to the first parameter, and is the same type as the expected value of the module call. The type of the return value is set every time Return is executed, which allows modules to return different types of values during execution if they are called (rather than launched).

This statement may appear inside or outside of a script, and like other statements that may be called from a state, if multiple calls are active simultaneously in a module, the return value will be invalid.

WARNING 1: Latching Behavior and If statements

If the Return statement is placed within a script block of a called module, and if that module is called by an If statement, then the return value will be reset to Invalid after the If statement executes. This is similar to the behavior of latching functions such as AbsTime() and Watch(). See example 2.

This behavior is not desirable for some called modules. The same goes for some modules that set their return value from script using SetReturnValue. Steady-state modules designed to avoid initial Invalid returns should invoke return functions with Resettable set to FALSE.

Warning 2: Returns, Constructors, and Invalids

If your module is being run as a subroutine and has a constructor, VTScada will return the value set by the constructor.

The return value of a callable module is usually Invalid initially. It is risky to watch for !Valid(CalledModule()) to indicate "Done".

In a called module with a constructor, the first state cannot have a steady-state Return statement, because if it did, the constructor's SetReturnValue would be considered a double-set and would return Invalid. You might move the Return to a script within the first state as follows.

SubReturn [
  If 1 Switch;
  [
    Return(GetReturnValue(Self), FALSE);
  ]
]

If the point is only to monitor for the return value of a callable module as a signal, a more reliable method is to use a previously declared variable.