matlab.metadata.Class Class

Namespace: matlab.metadata
Superclasses: matlab.metadata.MetaData

Describe MATLAB class

Renamed from meta.class in R2024a

Description

The matlab.metadata.Class class provides a way to get descriptive information about MATLAB^® classes. By creating a matlab.metadata.Class object for a specific class, you can get information about the class definition.

matlab.metadata.Class properties contain lists of properties, methods, events, and class attributes set in the classdef line, as well as other information about how the class is defined.

You cannot set the values of matlab.metadata.Class object properties. You can only query the properties.

Create a matlab.metadata.Class object from an instance of a class or using the class name using these options:

• metaclass(obj) returns a matlab.metadata.Class object representing the object passed as an argument.

• ?ClassName returns a matlab.metadata.Class object representing the named class.

• matlab.metadata.Class.fromName("ClassName") is a static method that returns a matlab.metadata.Class object representing the named class.

You cannot instantiate a matlab.metadata.Class object directly by calling its constructor.

The matlab.metadata.Class class is a handle class.

Class Attributes

Abstract	true
HandleCompatible	true

For information on class attributes, see Class Attributes.

Creation

Create a matlab.metadata.Class object from an instance of a class or using the class name using these options:

• metaclass(obj) returns a matlab.metadata.Class object representing the object passed as an argument.

• ?ClassName returns a matlab.metadata.Class object representing the named class.

• matlab.metadata.Class.fromName("ClassName") is a static method that returns a matlab.metadata.Class object representing the named class.

You cannot instantiate a matlab.metadata.Class object directly.

Properties

Name — Name of the class

character vector

Name of the class, returned as a character vector. The name returned by this property includes the class namespace.

Description — Short description of class

character vector

Short description of the class, returned as a character vector. For user-defined classes, the text for this property comes from comments in the class definition. If there are no comments, the property returns an empty character vector. For more information on how to include help text for your classes, see Custom Help Text.

DetailedDescription — Detailed description of class

character vector

Detailed description of the class, returned as a character vector. For user-defined classes, the text for this property comes from comments in the class definition. If there are no comments, the property returns an empty character vector. For more information on how to include help text for your classes, see Custom Help Text.

Hidden — Value of class attribute Hidden

false (default) | true

Is class hidden from inspection tools, returned as logical true or false. If true, the class does not appear in the output of MATLAB commands or tools that display class names. However, you can access the class programmatically.

Data Types: logical

Sealed — Value of class attribute Sealed

false (default) | true

Value of class attribute Sealed, returned as a logical value. If Sealed is true, this class cannot be subclassed.

Data Types: logical

Abstract — Value of class attribute Abstract

false (default) | true

Value of class attribute Abstract, returned as a logical value. The value of this property is true if the class or any property or method has its Abstract attribute set to true. For information on abstract classes, see Abstract Classes and Class Members.

Data Types: logical

Enumeration — Is class an enumeration class

false (default) | true

Is class an enumeration class, returned as a logical value. If true, this class is an enumeration class. For more information about enumeration classes, see Define Enumeration Classes.

Data Types: logical

ConstructOnLoad — Value of class attribute CustructOnLoad

false (default) | true

Value of class attribute ConstructOnLoad, returned as a logical value. If true, MATLAB calls the class constructor automatically when loading an object from a MAT-file. To enable ConstructOnLoad, the constructor must support being called with no input arguments. For more information, see Default Save and Load Process for Objects.

Data Types: logical

HandleCompatible — Value of class attribute HandleCompatible

false (default) | true

Value of class attribute HandleCompatible, returned as a logical value. If true, this class is a handle-compatible class. For more information about handle-compatible classes, see Handle Compatible Classes.

InferiorClasses — Value of class attribute InferiorClasses

matlab.metadata.Class object array

Value of class attribute InferiorClasses, returned as a matlab.metadata.Class object array. For information on class precedence, see Class Precedence.

Namespace — Namespace containing class

matlab.metadata.Namespace object

Namespace containing the class, returned as a matlab.metadata.Namespace object. If the class is not in a namespace, this property contains an empty matlab.metadata.Namespace object. For more information about namespaces, see Create Namespaces.

Aliases — List of aliases

string array

List of aliases defined for the class, returned as a string array. The aliases are listed from oldest to newest.

RestrictsSubclassing — Does class restrict subclassing

false (default) | true

Does class restrict subclassing, returned as a logical true or false. MATLAB sets this property to true when the class restricts subclassing by:

• Setting the Sealed attribute to true

• Specifying the classes that can subclass this class using the AllowedSubclasses attribute

For more information restricting subclassing, see Specify Allowed Subclasses.

PropertyList — Properties defined for the class

array of matlab.metadata.Property objects

Properties defined for the class, returned as an array of matlab.metadata.Property objects. The matlab.metadata.Property objects describe each property defined by this class, including all inherited public and protected properties. For more information on properties, see Properties.

MethodList — Methods defined for the class

array of matlab.metadata.Method objects

Methods defined for the class, returned as an array of matlab.metadata.Method objects. The matlab.metadata.Method objects describe each method defined by this class, including inherited public and protected methods. For more information on methods, see Methods in Class Design.

EventList — Events defined for the class

array of matlab.metadata.Event objects

Events defined for the class, including all inherited events, returned as an array of matlab.metadata.Event objects. Only handle classes can define events so this property is an empty matlab.metadata.Event object for value classes. All handle classes inherit the ObjectBeingDestroyed event. For more information about events, see Events.

EnumerationMemberList — Name and hidden status for enumeration members

array of matlab.metadata.EnumerationMember objects

Name and hidden status for enumeration members, returned as an array of matlab.metadata.EnumerationMember objects. Access the Name and Hidden properties of the corresponding member matlab.metadata.EnumerationMember object to obtain information. For more information, see Enumerations.

SuperclassList — Direct superclasses of this class

array of matlab.metadata.Class objects

Direct superclasses of this class, returned as an array of matlab.metadata.Class objects. The matlab.metadata.Class objects describe each direct superclass from which this class derives. For more information on subclassing, see Subclass Definition.

Methods

Public Methods

fromName

Return matlab.metadata.Class object that describes named class

Specialized Operators and Functions

These methods specialize standard MATLAB operators and functions for objects in this class.

eq (a == b)	Equality function (ClsA == ClsB). Use to test if two variables refer to equal classes (classes that contain exactly the same list of elements).
ne (a ~= b)	Not equal function (ClsA ~= ClsB). Use to test if two variables refer to different metaclasses.
lt (a < b)	Less than function (ClsA < ClsB). Use to determine if ClsA is a strict subclass of ClsB. A strict subclass means ClsX < ClsX is false.
le (a <= b)	Less than or equal to function (ClsA <= ClsB). Use to determine if ClsA is a subclass of ClsB.
gt (a > b)	Greater than function (ClsA > ClsB). Use to determine if ClsA is a strict superclass of ClsB. A strict superclass means ClsX > ClsX is false).
ge (a >= b)	Greater than or equal to function (ClsA >= ClsB). Use to determine if ClsA is a superclass of ClsB.

Events

Event Name	Trigger	Event Data	Event Attributes
InstanceCreated	This event occurs every time an instance of the class described by the matlab.metadata.Class is created. The event occurs immediately after all constructor functions finish executing.	event.ClassInstanceEvent	NotifyAccess: private ListenAccess: public
InstanceDestroyed	This event occurs every time an instance of the class described by the matlab.metadata.Class is destroyed. The event occurs immediately before any destructor functions execute.	event.ClassInstanceEvent	NotifyAccess: private ListenAccess: public

Examples

Use Introspection to Get Information About Classes

Use introspection to get inheritance information about the IntrospectionExample class.

classdef IntrospectionExample
    % IntrospectionExample  Performs basic functions on two numbers
    % Class methods find the sum and product of its properties.
    properties
        % a  First property
        % First of two numeric properties
        a {mustBeNumeric} = 0
        
        % b  Second property
        % Second of two numeric properties
        b {mustBeNumeric} = 0
    end
    
    methods
        function sum = addNumbers(obj)
            % addNumbers  Sum the properties
            %   Finds the sum of properties a and b.
            sum = obj.a + obj.b;
        end
        function prod = multNumbers(obj)
            % multNumbers  Multiply the properties
            %   Finds the product of properties a and b.
            prod = obj.a*obj.b;
        end
    end
end

Create a metaclass instance for IntrospectionExample.

mc = ?IntrospectionExample

mc = 

  Class with properties:

                    Name: 'IntrospectionExample'
             Description: 'Performs basic functions on two numbers'
     DetailedDescription: '  Class methods find the sum and product of its properties.'
                  Hidden: 0
                  Sealed: 0
                Abstract: 0
             Enumeration: 0
         ConstructOnLoad: 0
        HandleCompatible: 0
         InferiorClasses: [0×1 matlab.metadata.Class]
               Namespace: [0×0 matlab.metadata.Namespace]
                 Aliases: [0×1 string]
    RestrictsSubclassing: 0
            PropertyList: [2×1 matlab.metadata.Property]
              MethodList: [4×1 matlab.metadata.Method]
               EventList: [0×1 matlab.metadata.Event]
   EnumerationMemberList: [0×1 matlab.metadata.EnumerationMember]
          SuperclassList: [0×1 matlab.metadata.Class]

The property summary for IntrospectionExample shows there are four methods described in the MethodList property. Access the MethodList property of mc and display the names of all four class methods.

for i = 1:4
mc.MethodList(i).Name
end

ans = 
'multNumbers'

ans = 
'addNumbers'

ans = 
'IntrospectionExample'

ans = 
'empty'

Version History

Introduced in R2008a

R2024a: Namespace, class, method, and property renamed

The namespace, class name, static method, and one property of meta.class have been renamed. Their behavior remains the same.

• The new namespace is matlab.metadata.

• The new class name is Class.

• The static method meta.class.fromName is now matlab.metadata.Class.fromName.

• The ContainingPackage property is now Namespace.

MATLAB will continue to recognize the old metaclass names in most contexts. However, code that relies on string comparisons to identify metaclasses might need to be updated to continue to work as expected. For example, if mObj in the example below is a matlab.metadata.Class instance, the code under the case statement for 'meta.class' does not execute because class(mObj) returns 'matlab.metadata.Class'.

switch class(mObj)
   case 'meta.class'
       % code to execute if mObj is a meta.class instance
   ...
end

To ensure this code continues to work as intended, use an if statement with isa. The isa command recognizes both the old and new names of the class.

if isa(mObj,'meta.class') 
       % code to execute if mObj is a matlab.metadata.Class instance
   else
       ...
   end

If compatibility with older releases of MATLAB is not a concern, you can update 'meta.class' to 'matlab.metadata.Class'. However, continue to use the old name if your code needs to run on versions of MATLAB before R2024a.

R2022a: Description and DetailedDescription properties contain text from code comments

For user-defined classes with appropriately placed code comments, the Description and DetailedDescription properties are populated with text pulled from those comments. For more information on how to use code comments to store custom help text for user-defined classes, see Custom Help Text.

R2022a: Access class aliases from Aliases property

The Aliases property returns the aliases defined for the class.