Specify Value Class Objects as Inputs

You can specify that an input variable is an instance of a value class by using the MATLAB^® Coder™ app or by using the codegen command at the command line. In some cases, if the input variable is a user-written MATLAB class that contains property validation, you can use function argument validation to specify the input type. See Use User-Written MATLAB Classes in arguments Blocks. Code generation does not support handle class inputs to entry-point functions.

To specify a value class as an input type, the class definition must be in the working directory or on the MATLAB path.

• If you generate code by using the MATLAB Coder, you can define the value class input automatically or manually. When you choose to define a value class input manually, the app prompts you to enter a MATLAB command that generates an instance of the value class.

• If you generate code at the command line by using the codegen command, create an instance of the value class and pass this object to codegen by using the -args option.

Alternatively, you can create a type for an object of the value class at the command line by using coder.typeof or interactively by using the Coder Type Editor. See Create and Edit Input Types by Using the Coder Type Editor.

Example: Generate Code for an Entry-Point Function That Takes a Value Class Input

Consider the entry-point function calcArea, which takes an instance of the value class MyRectangle and multiplies the length and width properties of the MyRectangle object.

function out = calcArea(r) %#codegen
out = r.length*r.width;
end

Assume that the value class MyRectangle is defined in the working directory or on the MATLAB path.

classdef MyRectangle
    properties
        length (1,1) double
        width (1,1) double
    end
end

Generate Code by Using the MATLAB Coder App

Define calcArea as an entry-point function. Open the Entry Points pane and click Click to define data type next to input variable r. Type MyRectangle in the class definition box. The app prompts you to enter MATLAB code that produces a MyRectangle object. At this prompt, enter MyRectangle. The app determines the types of the length and width properties based on the class definition.

To generate code, click Generate Code in the MATLAB Coder toolstrip or in the Output section of the code generation sidebar.

Generate Code by Using the codegen command

Create an instance of the MyRectangle class at the command line and pass this instance to the codegen command.

myObj = MyRectangle

myObj = 

  MyRectangle with properties:

    length: 0
     width: 0

codegen calcArea -args {myObj} -report

Code generation successful: View report

Open the report and click the Variables tab. The input argument r has the same properties as the myObj object.

Consistency Between Type Definitions and Class Definition

When you generate code, the properties you define in the app or the properties of the object that you pass to the codegen must be consistent with the properties in the class definition file. However, if the class definition file has properties that your code does not use, the type definition does not have to include those properties. The code generator removes properties that you do not use.

Limitations for Using Objects as Entry-Point Function Inputs

Entry-point function inputs that are objects have these limitations:

• An object that is an entry-point function input must be an object of a value class. Objects of handle classes cannot be entry-point function inputs. Therefore, a value class that contains a handle class cannot be an entry-point function input.

• An object cannot be a global variable.

• If an object has duplicate property names, you cannot use it with coder.Constant. Duplicate property names occur in an object of a subclass in these situations:

  • The subclass has a property with the same name as a property of the superclass.

  • The subclass derives from multiple superclasses that use the same name for a property.

  For information about when MATLAB allows duplicate property names, see Subclassing Multiple Classes.