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Object is the base class that implements the *property* feature.
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A property is defined by a getter method (e.g. `getLabel`), and/or a setter method (e.g. `setLabel`). For example,
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the following getter and setter methods define a property named `label`:
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~~~
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private $_label;
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public function getLabel()
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{
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return $this->_label;
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}
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public function setLabel($value)
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{
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$this->_label = $value;
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}
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~~~
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Property names are *case-insensitive*.
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A property can be accessed like a member variable of an object. Reading or writing a property will cause the invocation
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of the corresponding getter or setter method. For example,
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~~~
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// equivalent to $label = $object->getLabel();
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$label = $object->label;
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// equivalent to $object->setLabel('abc');
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$object->label = 'abc';
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~~~
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If a property has only a getter method and has no setter method, it is considered as *read-only*. In this case, trying
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to modify the property value will cause an exception.
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One can call [[hasProperty()]], [[canGetProperty()]] and/or [[canSetProperty()]] to check the existence of a property.
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Besides the property feature, Object also introduces an important object initialization life cycle. In particular,
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creating an new instance of Object or its derived class will involve the following life cycles sequentially:
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1. the class constructor is invoked;
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2. object properties are initialized according to the given configuration;
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3. the `init()` method is invoked.
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In the above, both Step 2 and 3 occur at the end of the class constructor. It is recommended that
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you perform object initialization in the `init()` method because at that stage, the object configuration
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is already applied.
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In order to ensure the above life cycles, if a child class of Object needs to override the constructor,
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it should be done like the following:
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~~~
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public function __construct($param1, $param2, ..., $config = [])
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{
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...
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parent::__construct($config);
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}
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~~~
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That is, a `$config` parameter (defaults to `[]`) should be declared as the last parameter
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of the constructor, and the parent implementation should be called at the end of the constructor.
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