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Working with Meta-Classes

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What Are Meta-Classes?

What Are Meta-Classes?

Meta-classes are classes that contain information about class definitions. Each block in a class definition has an associated meta-class that defines the attributes for that block. Each attribute corresponds to a property in the meta-class. An instance of a meta-class has values assigned to each property that correspond to the values of the attributes of the associated class block.

Meta-classes enable programmatic inspection of classes and objects. Tools such as property inspectors, debuggers, and so on, use these techniques.

The meta Package

The meta package contains meta-classes that MATLAB uses for the definition of classes and class components. The class name indicates the component described by the meta-class:

meta.package
meta.class
meta.property
meta.method
meta.event

Each meta-class has properties, methods, and events that contain information about the class or class component. See meta.package, meta.class, meta.property, meta.method and meta.event for more information on these meta-classes.

Creating Meta-Class Objects

You cannot instantiate meta-classes directly by calling the respective class constructor. You can create meta-class objects from class instances or from the class name.

• ?ClassName — Returns a meta.class object for the named class. Use meta.class.fromName with class names stored as characters in variables.

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

• metaclass(obj) — Returns a meta-class object for the class instance (metaclass)

% create meta-class object from class name using the ? operator
mobj = ?classname; 
% create meta-class object from class name using the fromName method
mobj = meta.class.fromName('classname'); 
% create meta-class object from class instance
obj = myClass;
mobj = metaclass(obj); 

The metaclass function returns the meta.class object (that is, an object of the meta.class class). You can obtain other meta-class objects (meta.property, meta.method, and so on) from the meta.class object.

Note   Meta-class is a term used here to describe a kind of class. meta.class is a class in the meta package whose instances contain information about MATLAB classes.

Using Meta-Class Objects

Here is how you can use meta-class objects:

• Obtain a meta.class object from a class definition (using ?) or from a class instance (using metaclass).

• Use the meta.class properties, methods, and events to obtain information about the class or class instance from which you obtained the meta.class object. For example, get other meta-class objects, such as the meta.properties objects defined for each of the class properties.

The following examples show these techniques.

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Obtaining Information About Classes with Meta-Classes

Using Meta-Classes to Inspect Classes and Objects

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