meta.class class

Package: meta
Superclasses: meta.MetaData

Describe MATLAB class

Description

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

Some properties of a meta.class object contain the values of class attributes defined in the corresponding MATLAB class. Query these properties of to obtain information that is specified syntactically by the class definition on the classdef line.

Other properties contain lists of properties, methods, and events defined by the class, as well as other information about how the class is defined.

You cannot set the values of meta.class object properties. You can only query the properties.

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

• metaclass(obj) — returns a meta.class object representing the object passed as an argument.

• ?ClassName — returns a meta.class object representing the named class.

• meta.class.fromName('ClassName') — static method returns a meta.class object representing the named class.

You cannot instantiate a meta.class object directly by calling its constructor.

The meta.class class is a handle class.

Class Attributes

Abstract

true

For information on class attributes, see Class Attributes.

Properties

Abstract — Value of class abstract attribute

false (default) | true

Value of class abstract attribute, 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.

Example: classdef (Abstract = true) ...

Data Types: logical

ConstructOnLoad — Call constructor on load

false (default) | true

Call constructor on load, 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 Save and Load Process for Objects.

Example: classdef (ConstructOnLoad = true) ...

Data Types: logical

ContainingPackage — Package containing class

meta.package

Package containing class, returned as a meta.package object. If the class is not in a package this property contains an empty meta.package object. For more information about packages, see Packages Create Namespaces.

Data Types: meta.package

Description — Currently not used

information from class comments

Currently not used to collect information about the class from comments.

Data Types: char | string

DetailedDescription — Currently not used

information from class comments

Currently not used to collect information about the class from comments.

Data Types: char | string

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

EnumerationMemberList — Name and hidden status for enumeration members

meta.EnumeratedValue array

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

Data Types: meta.EnumeratedValue

EventList — Events defined for the class

meta.event array

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

Data Types: meta.event

Hidden — Is class hidden from inspection tools

false (default) | true

Is class hidden from inspection tools, returned as logical true or false. When set to 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

InferiorClasses — Classes specified as inferior to this class

cell array of meta.class objects

Classes specified as inferior to this class, returned as a cell array of meta.class objects. For information on class precedence, see Class Precedence.

Example: classdef (InferiorClasses = {?ClassName1,?ClassName2}) ...

Data Types: meta.class

MethodList — Methods defined for the class

array of meta.method objects

Methods defined for the class, returned as an array of meta.method objects. The meta.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.

Data Types: meta.method

Name — Name of the class

character vector

Name of the class, returned as a character vector. The class name returned by this property does not include any packages that contain the class.

Data Types: char

PropertyList — Properties defined for the class

array of meta.property objects

Properties defined for the class, returned as an array of meta.property objects describing each property, including all inherited public and protected properties. For more information on properties, see Properties.

Data Types: meta.property

RestrictsSubclassing — Does class restricts subclassing

false (default) | true

Does class restrict subclassing, returned as a logical true or false. MATLAB sets this attribute 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.

Example: classdef (AllowedSubclasses = {?ClassName1,?ClassName2}) ...

Data Types: logical

Sealed — Can class be subclassed

false (default) | true

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

Example: classdef (Sealed = true) ...

Data Types: logical

SuperclassList — Direct superclasses of this class

meta.class array

Direct superclasses of this class, returned as an array of meta.class objects describing each direct superclass from which this class derives. For more information subclassing, see Subclass Definition.

Example: classdef MyClass < MySuperclass & MyMixin

Data Types: meta.class

Methods

Public Methods

fromName

Return meta.class object associated with 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 meta–classes.
lt (a < b)	Less than function (ClsA < ClsB). Use to determine if ClsA is a strict subclass of ClsB (i.e., 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 (i.e., 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 meta.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 meta.class is destroyed. The event occurs immediately before any destructor functions execute.	event.ClassInstanceEvent	NotifyAccess: private ListenAccess: public

Examples

Find Property Attribute

Find property attributes using the handle class findobj method and the audioplayer meta.class object. Determine if you can change the SampleRate property on an audioplayer object.

Create an audioplayer object.

load('handel.mat')
player = audioplayer(y,Fs);

Get the meta.class object for the audioplayer object.

mc = metaclass(player);

Get the meta.property object for the SampleRate property.

mp = findobj(mc.PropertyList,'Name','SampleRate');

Use the meta.property object to determine if the SampleRate property can be modified. If SetAccess is public, set the SampleRate property.

if strcmp(mp.SetAccess,'public')
   player.SampleRate = 7200;
end