Main Content

Specify Objects as Inputs at the Command Line

If you generate code by using codegen, to specify the type of an input that is a value class object, you can provide an example object with the -args option.

  1. Define the value class. For example, define a class myRectangle.

    classdef myRectangle
            function obj = myRectangle(l,w)
                if nargin > 0
                    obj.length = l;
                    obj.width = w;
            function area = calcarea(obj)
                area = obj.length * obj.width;

  2. Define a function that takes an object of the value class as an input. For example:

    function z = getarea(r)
    z = calcarea(r);

  3. Create an object of the class.

    rect_obj = myRectangle(4,5)

    rect_obj = 
      myRectangle with properties:
        length: 4
         width: 5
  4. Pass the example object to codegen by using the -args option.

    codegen getarea -args {rect_obj} -report

    In the code generation report, you see that r has the same properties, length and width, as the example object rect_object. The properties have the same size and type as they do in the example object, rect_object.

    Code generation report window, showing properties length and width of myRectangle object r

Instead of providing an example object, you can create a type for an object of the value class, and then provide the type with the -args option.

  1. Create an object of the class:

    rect_obj = myRectangle(4,5)
    rect_obj = 
      myRectangle with properties:
        length: 4
         width: 5

  2. To create a type for an object of myRectangle that has the same property types as rect_obj, use coder.typeof.

    coder.typeof creates a coder.ClassType object that defines a type for a class.

    t= coder.typeof(rect_obj)
    t = 
       1×1 myRectangle   
          length: 1×1 double
          width : 1×1 double

  3. Pass the type to codegen by using the -args option.

    codegen getarea -args {t} -report

After you create a type for a value class, you can change the types of the properties. For example, to make the properties of t 16-bit integers:

t.Properties.length = coder.typeof(int16(1))
t.Properties.width = coder.typeof(int16(1))

You can also add or delete properties. For example, to add a property newprop:

t.Properties.newprop = coder.typeof(int16(1))

Consistency Between coder.ClassType Object and Class Definition File

When you generate code, the properties of the coder.ClassType object that you pass to codegen must be consistent with the properties in the class definition file. If the class definition file has properties that your code does not use, the coder.ClassType object 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.

See Also

Related Topics