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MATLAB Classes Definition for Code Generation

To generate efficient standalone code for MATLAB® classes, you must use classes differently than when running your code in the MATLAB environment.

Language Limitations

Although code generation support is provided for common features of classes such as properties and methods, there are a number of advanced features which are not supported, such as:

  • Events

  • Listeners

  • Arrays of objects

  • Recursive data structures

    • Linked lists

    • Trees

    • Graphs

  • Nested functions in constructors

  • Overloadable operators subsref, subsassign, and subsindex

    In MATLAB, classes can define their own versions of the subsref, subsassign, and subsindex methods. Code generation does not support classes that have their own definitions of these methods.

  • The empty method

    In MATLAB, classes have a built-in static method, empty, which creates an empty array of the class. Code generation does not support this method.

  • The following MATLAB handle class methods:

    • addlistener

    • eq

    • findobj

    • findprop

  • The AbortSet property attribute

Code Generation Features Not Compatible with Classes

  • You can generate code for entry-point MATLAB functions that use classes, but you cannot generate code directly for a MATLAB class.

    For example, if ClassNameA is a class definition, you cannot generate code by executing:

    codegen ClassNameA

  • A handle class object cannot be an entry-point function input or output.

  • A value class object can be an entry-point function input or output. However, if a value class object contains a handle class object, then the value class object cannot be an entry-point function input or output. A handle class object cannot be an entry-point function input or output.

  • Code generation does not support global variables that are handle classes.

  • Code generation does not support multiple outputs from constructors.

  • Code generation does not support assigning an object of a value class into a nontunable property. For example, obj.prop=v; is invalid when prop is a nontunable property and v is an object based on a value class.

  • You cannot use coder.extrinsic to declare a class or method as extrinsic.

  • If an object has duplicate property names and the code generator tries to constant-fold the object, code generation can fail. The code generator constant-folds an object when it is used with coder.Constant or coder.const, or when it is an input to or output from a constant-folded extrinsic function.

    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.

    Duplicate property names must be consistently constant or non-constant across multiple inheritance related classes. For example, code generation produces an error if an object with a constant property aProp inherits aProp from a superclass where aProp is defined as non-constant.

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

Defining Class Properties for Code Generation

For code generation, you must define class properties differently than you do when running your code in the MATLAB environment:

  • To test property validation, it is a best practice to run a MEX function over the full range of input values.

  • After defining a property, do not assign it an incompatible type. Do not use a property before attempting to grow it.

    When you define class properties for code generation, consider the same factors that you take into account when defining variables. In the MATLAB language, variables can change their class, size, or complexity dynamically at run time so you can use the same variable to hold a value of varying class, size, or complexity. C and C++ use static typing. Before using variables, to determine their type, the code generator requires a complete assignment to each variable. Similarly, before using properties, you must explicitly define their class, size, and complexity.

  • Initial values:

    • If the property does not have an explicit initial value, the code generator assumes that it is undefined at the beginning of the constructor. The code generator does not assign an empty matrix as the default.

    • If the property does not have an initial value and the code generator cannot determine that the property is assigned prior to first use, the software generates a compilation error.

    • For System objects, if a nontunable property is a structure, you must completely assign the structure. You cannot do partial assignment using subscripting.

      For example, for a nontunable property, you can use the following assignment:


      You cannot use the following partial assignments:

      mySystemObject.nonTunableProperty.fieldA = 'a';
      mySystemObject.nonTunableProperty.fieldB = 'b';

    • coder.varsize is not supported for class properties.

    • If the initial value of a property is an object, then the property must be constant. To make a property constant, declare the Constant attribute in the property block. For example:

      classdef MyClass 
          properties (Constant) 
              p1 = MyClass2; 

      Code generation does not support a constant property that is assigned to an object that contains a System object™.

    • MATLAB computes class initial values at class loading time before code generation. If you use persistent variables in MATLAB class property initialization, the value of the persistent variable computed when the class loads belongs to MATLAB; it is not the value used at code generation time. If you use in MATLAB class property initialization,'MATLAB') returns true (1).

  • Variable-size properties:

    • Code generation supports upper-bounded and unbounded variable-size properties for both value and handle classes.

    • To generate unbounded variable-size class properties, enable dynamic memory allocation.

    • To make a variable-size class property, make two sequential assignments of a class property, one to a scalar and the next to an array.

      classdef varSizeProp1 < handle
      function extFunc(n)
          obj = varSizeProp1;    
          % Assign a scalar value to the property.
          obj.prop = 1;
          obj.varProp = 1;
          % Assign an array to the same property to make it variable-sized.
          obj.prop = 1:98;    
          obj.varProp = 1:n;

      In the preceding code, the first assignment to prop and varProp is scalar, and their second assignment is to an array with the same base type. The size of prop has an upper bound of 98, making it an upper-bounded, variable-size property.

      If n is unknown at compile time, obj.varProp is an unbounded variable-size property. If it is known, it is an upper-bounded, variable-size class property.

    • If the class property is initialized with a variable-size array, the property is variable-size.

      classdef varSizeProp2 
              function obj = varSizeProp2(inVar)
                  % Assign incoming value to local variable
                  locVar = inVar;
                  % Declare the local variable to be a variable-sized column             
                  % vector with no size limit
                  coder.varsize('locVar',[inf 1],[1 0]);
                  % Assign value
                  obj.prop = locVar;

      In the preceding code, inVar is passed to the class constructor and stored in locVar. locVar is modified to be variable-size by coder.varsize and assigned to the class property obj.prop, which makes the property variable-size.

      • If the input to the function call varSizeProp2 is variable-size, coder.varsize is not required.

        function z = constructCall(n)
            z = varSizeProp2(1:n);
      • If the value of n is unknown at compile-time and has no specified bounds, z.prop is an unbounded variable-size class property.

      • If the value of n is unknown at compile-time and has specified bounds, z.prop is an upper-bounded variable-size class property.

  • If a property is constant and its value is an object, you cannot change the value of a property of that object. For example, suppose that:

    • obj is an object of myClass1.

    • myClass1 has a constant property p1 that is an object of myClass2.

    • myClass2 has a property p2.

    Code generation does not support the following code:

    obj.p1.p2 = 1;

Inheritance from Built-In MATLAB Classes Not Supported

You cannot generate code for classes that inherit from built-in MATLAB classes. For example, you cannot generate code for the following class:

classdef myclass < double

An exception to this rule is the MATLAB enumeration class. You can generate code for enumeration classes that inherit from built-in MATLAB classes. See Code Generation for Enumerations (MATLAB Coder).

See Also

Related Topics