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meta.property class

Package: meta
Superclasses: meta.MetaData

Describe property of MATLAB class

Description

The meta.property class provides information about the properties of MATLAB® classes. Properties of the meta.property class contain the values of property attributes and other information that is specified syntactically in the class definition. All properties are read-only.

The meta.property class is a handle class.

Class Attributes

Abstract
true
ConstructOnLoad
true

For information on class attributes, see Class Attributes.

Creation

You cannot instantiate a meta.property object directly. Obtain a meta.property object from the meta.class PropertyList property, which contains an array of meta.property objects, one for each class property. For example, replace ClassName with the name of the class whose properties you want to query:

mco = ?ClassName;
plist = mco.PropertyList;
mp = plist(1); % meta.property for first property in list

Use the metaclass function to obtain a meta.class object from a class instance:

mco = metaclass(obj);

Properties

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Property name, returned as a character vector. The meta.property Name property corresponds to the name of the associated property defined by the class.

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

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

The read (get) access level of the property, returned as:

  • public — unrestricted access

  • protected — access from class or subclasses

  • private — access by class members only (not from subclasses)

  • List of classes that have read access to this property, specified as meta.class objects in the form:

    • A single meta.class object.

    • A cell array of meta.class objects. An empty cell array, {}, is the same as private access.

For more information, see Class Members Access.

Data Types: enumerated | meta.class

The write (set) access level of the property, returned as:

  • public — unrestricted access

  • protected — access from class or subclasses

  • private — access by class members only (not from subclasses)

  • immutable — property can only be set by constructor. For more information, see Mutable and Immutable Properties.

  • List of classes that have write access to this property, specified as meta.class objects in the form:

    • A single meta.class object.

    • A cell array of meta.class objects. An empty cell array, {}, is the same as private access.

For more information, see Class Members Access.

Data Types: enumerated | meta.class

Does the property value depend on other values, returned as logical true or false. If false (the default), the property value is stored in the object. If true, the property value is not stored in the object, and the set and get functions cannot access the property by indexing into the object using the property name. Dependent properties must define access methods. For more information, see Set and Get Methods for Dependent Properties.

Is the property value constant, returned as logical true or false. If true, this property has the same value in all instances of the class. For more information, see Define Class Properties with Constant Values.

Is the property abstract, returned as logical true or false. If true, the property has no implementation and the class is abstract. For more information, see Abstract Classes and Class Members.

Is the property saved with the object, returned as logical true or false. If true, the property value is not saved when the object is saved to a MAT file. For more information about saving objects, see Save and Load Process for Objects.

Is the property hidden from the property list, returned as logical true or false. Hidden determines if the property is shown in a property list (as a result of a call to properties, for example). Hidden properties are not shown in the default object display.

Can listeners receive property get events, returned as logical true or false. If true, and it is a handle class property, then you can create listeners that execute when the property value is queried. MATLAB calls the listeners whenever property values are queried. For more information, see Property-Set and Query Events.

Can listeners receive property set events, returned as logical true or false. If true, and it is a handle class property, then you can create listeners that execute when the property value is set. MATLAB calls the listeners whenever property values are modified. For more information, see Property-Set and Query Events.

Is property set if value is unchanged, returned as logical true or false. If true, then setting a property value is aborted if the new value is the same as the current value. If the property belongs to a handle class, setting AbortSet to true prevents the triggering of property PreSet and PostSet events.

Is the property copyable, returned as logical true or false. If false, the property value is copied when the object is copied (handle class only). By default, copying a handle object copies the concrete properties of that object. For more information, see Exclude Properties from Copy.

Priority for partial name matching, returned as a numeric value. Use with subclasses of matlab.mixin.SetGet to define the relative priority of partial property name matches used in set and get method arguments. The default value is 1. Greater values assign lower priorities. For more information, see Set Priority for Matching Partial Property Names.

Property get method, returned as a function handle or an empty value. Function handle of the get method associated with this property. The value is empty if there is no get method specified in the class definition. For more information, see Property Get Methods.

Property set method, returned as a function handle or an empty value. Function handle of the set method associated with this property. The value is empty if there is no set method specified in the class definition. For more information, see Property Set Methods

Does the property define a default value, returned as logical true or false. If true, the property defines a default value in the class definition. Test HasDefault before querying the DefaultValue property to avoid a MATLAB:class:NoDefaultDefined error.

Data Types: logical

Default value specified in the class definition. Abstract, dependent, and dynamic properties cannot specify default values.

If there is no default value in the class definition, MATLAB does not display the DefaultValue property. Test HasDefault before querying the DefaultValue property to avoid a MATLAB:class:NoDefaultDefined error.

Validation defined for property, returned as a meta.Validation object. This property contains a meta.Validation object describing the validation defined by this property. If the property does not define validation, this property contains an empty meta.Validation object.

Class that defines the property, returned as a meta.class object. The meta.class object represents the class that defines this property, which can be a superclass.

Events

Event NameTriggerEvent DataEvent Attributes
PreGetEvent occurs just before the property value is queried.event.PropertyEvent

NotifyAccess: private

ListenAccess: public

PostGetEvent occurs just after the property value has been queried.event.PropertyEvent

NotifyAccess: private

ListenAccess: public

PreSetEvent occurs just before the property value is changed.event.PropertyEvent

NotifyAccess: private

ListenAccess: public

PostSetEvent occurs just after the property value has been changed.event.PropertyEvent

NotifyAccess: private

ListenAccess: public

Examples

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Use meta.property to get information about a class property of the IntrospectionExample class.

Code for IntrospectionExample

classdef IntrospectionExample
    % IntrospectionExample  Performs basic functions on two numbers
    % This class can return the sum and product of its two 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 and Inspect a Metaclass Instance

Create a metaclass instance for IntrospectionExample. Access the first property in the PropertyList of mc to get a meta.property object.

mc = ?IntrospectionExample;
mc.PropertyList(1)
ans = 
  property with properties:

                    Name: 'a'
             Description: 'First property'
     DetailedDescription: '  First of two numeric properties'
               GetAccess: 'public'
               SetAccess: 'public'
               Dependent: 0
                Constant: 0
                Abstract: 0
               Transient: 0
                  Hidden: 0
           GetObservable: 0
           SetObservable: 0
                AbortSet: 0
             NonCopyable: 0
    PartialMatchPriority: 1
               GetMethod: []
               SetMethod: []
              HasDefault: 1
            DefaultValue: 0
              Validation: [1x1 meta.Validation]
           DefiningClass: [1x1 meta.class]

Check what validation the class performs on the property value.

mc.PropertyList(1).Validation
ans = 
  Validation with properties:

                 Class: [0x0 meta.class]
                  Size: [1x0 meta.ArrayDimension]
    ValidatorFunctions: {@mustBeNumeric}

Version History

Introduced in R2008a

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