Using Caché ObjectScript - InterSystems Documentation

User-defined Code
• Caché saves the current value of the system variable $TEST when it enters the function and restores it when the function
terminates. Any change in the $TEST value during execution of the function will be discarded when the function exits,
unless you include code to explicitly save it by some other means.
8.3.2.6 Location of Functions
You can define a user-defined function within the routine that references it, or in a separate routine where multiple programs
can reference it. Recommended practice is to use one routine to contain all your user-defined function definitions. In this
way, you can easily locate any function definition to examine or update it.
8.3.2.7 Invoking a User-defined Function
You can invoke a user-defined function using either the $$ prefix, or by using the Do command. The $$ form provides the
most functionality, and is generally the preferred form.
Using the $$ Prefix
You can invoke a user-defined function in any context in which an expression is allowed. A user-defined function call takes
the form:
$$name([param [,...]])
where
• name specifies the name of the function. Depending on where the function is defined, name can be specified as:
– label — A line label within the current routine.
– label^routine — A line label within the named routine that resides on disk.
– ^routine — A routine that resides on disk. The routine must contain only the code for the function to be performed.
A routine is defined within a namespace. You can use an extended routine reference to execute a user-defined function
that is located in a routine defined in a namespace other than the current namespace:
WRITE $$myfunc^|"SAMPLES"|routine
• param specifies the values to be passed to the function. The supplied parameters are known as the actual parameter
list. They must match the formal parameter list defined for the function. For example, the function code may expect
two parameters, with the first being a numeric value and the second being a string literal. If you specify the string literal
for the first parameter and the numeric value for the second, the function may yield an incorrect value or possibly
generate an error. Parameters in the formal parameter list always have New invoked by the function. See the New
command. Parameters can be passed by value or by reference. See Parameter Passing. If you pass fewer parameters
to the function than are listed in the function’s formal parameter list, parameter defaults are used (if defined); if there
are no defaults, these parameters remain undefined.
Using the Do Command
You can invoke a user-defined function using the Do command. (You cannot invoke a system-supplied function using the
Do command.) A function invoked using Do does not return a value. That is, the function must generate a return value, but
the Do command ignores this return value. This greatly limits the use of Do for invoking user-defined functions.
To invoke a user-defined function using Do, you issue a command in the following syntax:
Do label(param[ ,...])
90 Using Caché ObjectScript