Function Statement

Makes a private procedure that returns a value.

Syntax

Usual construct

[ modifiers ] _
Function function_name [ type_list ] [ parameter_list ] [ return_type ]
    [ Where generic_constraints ]
    [ statements ]
End [ Function ]

Name-change construct

[ modifiers ] _
Function function_name Does trait_name . supplied_name

Parts

modifiers
Optional
  • @Iterator – The procedure implements the iterator pattern. See @Iterator.
  • @Shared – only procedures in the same scope that are also @Shared can call the procedure.
function_name
Mandatory name for the function.
type_list
Optional one or more names with a comma between each, all between brackets ([ ]). See Type List for more information.
Not permitted in the name-change construct.
parameter_list
Optional in the usual construct. One or more local variables with a comma between each. The caller gives them their values. The modifier ByRef is not permitted. See Parameter List for more information.
Not permitted in the name-change construct.
return_type
Optional if function_name has a type character. See Type Characters for more information.
Mandatory if function_name does not have a type character.
Not permitted in the name-change construct.

Return type

As type
or
In unit
type
A data type
unit
A unit of measure
generic_constraints
Optional. See Where Clause (Generics) for more information.
statements
In the usual construct, optional one or more statements to declare elements and/or run some code.
Not permitted in the name-change construct.
End
Completes the statement. You can also use End Function.
You can change this part of the syntax. See @Option Directive for more information.
Not permitted in the name-change construct.
trait_name
In the name-change construct, mandatory name of a trait that the class or object applies.
supplied_name
In the name-change construct, mandatory name of a procedure supplied by a trait.

Instructions

End Function is not the same as Exit Function.

A function is a type of procedure that has many limits. It is at the core of functional programming. These limits include:

A function has the qualities that follow:

Defining a function

You can put a function only in a class, structure, trait, or module. You cannot put a function in a different procedure, or in a loop.

Functions have the private access level. You can call a function only from the same object or module in which it is declared. If public access is necessary, use a method.

You must specify the data type that a function returns. You usually use one of the keywords As or In after the right parenthesis. Alternatively, you can supply a name with a type character (examples are i%, r!, or s$). If you do not specify a data type, this will cause an error.

Returning from a function

Function Sum(a As Real64, b As Real64) As Real64
    Return a + b
End Function

Function Sum(a As Real64, b As Real64) As Real64
    Sum = a + b
    Exit Function
End Function

Calling a function

Dim result As Real64
result = Sum(14.0, 28.0)

Examples

TODO

See also