Propeller Manual

2: Spin Language Reference – PUB
Propeller Manual v1.1 · Page 183
Public Method Declaration
Public Method declarations begin with
PUB, in column 1 of a line, followed a unique name
and an optional set of parameters, a result variable, and local variables.
Example:
PUB Init
<initialization code>
PUB MotorPos : Position
Position := <code to retrieve motor position>
PUB MoveMotor(Position, Speed) : Success | PosIndex
<code that moves motor to Position at Speed and returns True/False>
This example contains three public methods, Init, MotorPos and MoveMotor. The Init
method has no parameters and declares no return value or local variables. The
MotorPos
method has no parameters but declares a return value called
Position. The MoveMotor
method has two parameters,
Position and Speed, a return value, Success, and a local variable,
PosIndex.
All executable statements that belong to a
PUB method appear underneath its declaration,
indented by at least one space.
The Return Value
Whether or not a
PUB declaration specifies an RValue , there is always an implied return value
that defaults to zero (0). There is a pre-defined name for this return value within every
PUB
method, called
RESULT. At any time within a method, RESULT can be updated like any other
variable and, upon exiting the method, the current value of
RESULT will be passed back to the
caller. In addition, if a
RESULT is declared for the method, that name can be used
interchangeably with the built-in
T
RESULTT variable. For instance, the MotorPos method above
sets “
Position := …” and could also have used “Result := …” for the same effect. Despite
this, it is considered good practice to give a descriptive name to the return value (in the
PUB
declaration) for any method whose return value is significant. Likewise, it is good practice to
leave the return value unnamed (in the
PUB declaration) for any method whose return value is
unimportant and unused.