Main Content

Call the Methods of a Class Instance

Standard Mapping Technique

After you create a class instance, you can call the class methods to access the encapsulated MATLAB® functions. The MATLAB Compiler SDK™ product uses a standard technique to map the original MATLAB function syntax to the method's argument list. This standard mapping technique is as follows:

  • nargout

    When a method has output arguments, the first argument is always nargout, which is of type Long. This input parameter passes the normal MATLAB nargout parameter to the encapsulated function and specifies how many outputs are requested. Methods that do not have output arguments do not pass a nargout argument.

  • Output parameters

    Following nargout are the output parameters listed in the same order as they appear on the left side of the original MATLAB function.

  • Input parameters

    Next come the input parameters listed in the same order as they appear on the right side of the original MATLAB function.

For example, the most generic MATLAB function is: 

function [Y1, Y2, ..., varargout] = foo(X1, X2, ..., varargin)

This function maps directly to the following Microsoft® Visual Basic® signature:

Sub foo(nargout As Long, _
        Y1 As Variant, _
        Y2 As Variant, _
        .
        .
        varargout As Variant, _
        X1 As Variant, _
        X2 As Variant, _
        .
        .
        varargin As Variant)

See Calling Conventions for more details and examples of the standard mapping from MATLAB functions to COM class method calls.

Variant

All input and output arguments are typed as Variant, the default Visual Basic data type. The Variant type can hold any of the basic Visual Basic types, arrays of any type, and object references. See Data Conversion for details about the conversion of any basic type to and from MATLAB data types.

In general, you can supply any Visual Basic type as an argument to a class method, with the exception of Visual Basic User Defined Types (UDTs).

When you pass a simple Variant type as an output parameter, the called method allocates the received data and frees the original contents of the Variant. In this case it is sufficient to dimension each output argument as a single Variant. When an object type (like an Excel® Range) is passed as an output parameter, the object reference is passed in both directions, and the object's Value property receives the data.

Pass Input and Output Parameters

The following examples show how to pass input and output parameters to COM component class methods in Visual Basic.

The first example is a function, foo, that takes two arguments and returns one output argument. The foo function dispatches a call to a class method that corresponds to a MATLAB function of the form function y = foo(x1,x2).

Function foo(x1 As Variant, x2 As Variant) As Variant
   Dim aClass As Object
   Dim y As Variant
   
   On Error Goto Handle_Error
   Set aClass = CreateObject("mycomponent.myclass.1_0")
   Call aClass.foo(1,y,x1,x2)
   foo = y
   Exit Function
Handle_Error:
   foo = Err.Description
End Function

The second example rewrites the foo function as a subroutine:

Sub foo(Xout As Variant, X1 As Variant, X2 As Variant)
   Dim aClass As Object

   On Error Goto Handle_Error
   Set aClass = CreateObject("mycomponent.myclass.1_0")
   Call aClass.foo(1,Xout,X1,X2)
   Exit Sub
Handle_Error:
   MsgBox(Err.Description)
End Sub