Chapter 4: Object Advanced Features

• Static Methods and Properties
• Constant Properties
• Abstract Classes(extends)
  • [Error]PHP Fatal error: Cannot instantiate abstract class ShopProductWriter in…
  • [Error]PHP Fatal error: Class ErroredWriter contains 1 abstract method and
• Interfaces (implements)
• Traits (use)
  • Using More than One Trait
  • Managing Method Name Conflicts with insteadof
    • [Error]Fatal error: Trait method calculateTax has not been applied
    • use PriceUtilities, TaxTools {TaxTools::calculateTax insteadof PriceUtilities;}
  • Defining Abstract Methods in Traits
    • it takes on the commitment to implement any abstract methods it declares
  • Changing Access Rights to Trait Methods (p53)
    • as operator can be used to alias a method name
    • use an access modifier on the right-hand side of this operator, it will change the method’s access level
      • PriceUtilities::calculateTax as private;
• Late Static Bindings: The static Keyword (p55)
  • (1)static. static is similar to self, except that it refers to the invoked rather than the containing class.
    • return new static();
  • (2) The static keyword can be used for more than just instantiation Like self and parent $this->group = static::getGroup(); (p56)
• Handling Errors
  • Throwing an Exception, try/catch Clauses, with finally
    • throw new Exception( “file ‘$file’ does not exist” );
• Final Classes and Methods
  • final puts a stop to inheritance. A final class cannot be subclassed. Less drastically, a final method cannot be overridden.
  • [Error] PHP Fatal error: Class IllegalCheckout may not inherit from final class (Checkout) in
  • [Error] Fatal error: Cannot override final method Checkout::totalize() in …
• Working with Interceptors

• Defining Destructor Methods
  • function __destruct()
• Copying Objects with __clone()
  • (1)clone operates on an object instance, producing a by-value copy
    • $second = clone $first;
    • __clone() is run on the copied object and not the original; overwrites the default copy
• Defining String Values for Your Objects
  • [Error] PHP Catchable fatal error: Object of class StringThing could not be converted to string in
  • By implementing a __toString() method
• Callbacks, Anonymous Functions and Closures
  • is_callable(), call_user_func(), array_walk()
  • [ugly]$logger = create_function( ‘$product’, ‘print “ logging ({$product->name})\n”;’ );
  • [PHP 5.3] $logger2 = function( $product ) { print “ logging ({$product->name})\n”; }
  • [return anonymous fun] return function( $product ) use ( $amt, &$count ){…} (p79)

Chapter 5: Object Tools

• PHP and Packages
  • avoid naming collisions [p82]
    • [Error]PHP Fatal error: Cannot redeclare class Outputter in …Outputter1.php on line 2
    • [problem] as projects got more involved in class name, class names grew longer and longer.
  • Namespaces to the Rescue [PHP 5.3]
    • namespace com\getinstance\util
      • [Error] PHP Fatal error: Class ‘main\com\getinstance\util\Debug’ not found in…
      • [Solution]Search Gloable: That leading backslash tells PHP to begin its search at the root
      • \com\getinstance\util\Debug::helloWorld();
    • implicitly aliased
      • use com\getinstance\util;
      • util\Debug::helloWorld();
      • [Notice] that I didn’t begin with a leading backslash character
    • name collisions [alias explicit]
      • [Error] PHP Fatal error: Cannot declare class main\Debug because the name is already in use in…
      • [Solution]alias explicit: use com\getinstance\util\Debug as uDebug;
    • __NAMESPACE__
    • [Alternative Format]namespace com\getinstance\util {}
• The Class and Object Functions
  • Looking for Classes
    • class_exists()
      • $path = “tasks/{$classname}.php”
      • if ( ! file_exists( $path ) ) {…}
  • Learning About an Object or Class
    • get_class()
    • if ( get_class( $product ) === ‘CdProduct’ ) {…}
  • Getting a Fully Qualified String Reference to a Class
    • ClassName::class
    • a scope resolution operator and the class keyword to get the fully qualified class name
  • Learning About Methods
    • get_class_methods()
      • [Useful Case]if ( in_array( $method, get_class_methods( $product ) ) )
      • then invoke $product->$method()
    • is_callable()
      • if ( is_callable( array( $product, $method) ) )
    • method_exists()
      • if ( method_exists( $product, $method ) )
      • [Caution] remember that the fact that a method exists does not mean that it will be callable
      • [Caution] returns true for private and protected methods as well as for public ones.
  • Learning About Properties
    • get_class_vars( ‘CdProduct’ )
      • print_r( get_class_vars( ‘CdProduct’ ) );
  • Learning About Inheritance
    • get_parent_class()
      • if ( is_subclass_of( $product, ‘ShopProduct’ ) )
    • is_subclass_of()
      • if ( in_array( ‘someInterface’, class_implements( $product )) )
  • Method Invocation
    • [1]$product->$method();
    • [2]call_user_func()
      • $returnVal = call_user_func( array( $myObj, “methodName”) )
      • call_user_func( array( $product, ‘setDiscount’ ), 20 );
        • $product->setDiscount( 20 );
      • call_user_func_array()
• The Reflection API

• Time to Roll Up Your Sleeves(p99)
  • Reflection::export();
    • $prod_class = new ReflectionClass( ‘CdProduct’ );
    • Reflection::export( $prod_class );
    • [Notice] var_dump(): it provides nothing like the detail made available by Reflection::export()
    • [Notice] print_r(): var_dump’s cousin
  • ReflectionClass::getName()
    • $class->getName()
  • ReflectionClass::isUserDefined()
    • $class->isUserDefined()
  • ReflectionClass::isInternal()
    • $class->isInternal()
  • ReflectionClass::isAbstract()
    • $class->isAbstract()
  • ReflectionClass::isInterface()
    • $class->isInterface()
  • ReflectionClass::isInstantiable()
    • $class->isInstantiable()
  • ReflectionClass::getFileName()
    • $lines = @file( $class->getFileName() );
  • $class->getStartLine();
• Examining Methods (p103)
  • ReflectionClass::getMethods()
    • $prod_class = new ReflectionClass( ‘CdProduct’ );
    • $methods = $prod_class->getMethods();
  • ReflectionClass::
    • getName(), isInternal(), isAbstract(), isPublic(), isProtected(), isPrivate(), isStatic9(), isFinal(), isConstructor(), returnsReference()
  • ReflectionMethod::invoke() (p108)
• Examining Method Arguments (p104)
  • ReflectionMethod::getParameters()
    • $prod_class = new ReflectionClass( ‘CdProduct’ );
    • $method = $prod_class->getMethod( “__construct” );
    • $params = $method->getParameters()
  • $arg->getPosition()
  • $arg->isPassedByReference()
  • $arg->isDefaultValueAvailable()
• Using the Reflection API (p105)
  • plug-ins written
    • To achieve this, you might define an execute() method in the Module interface or abstract base class, forcing all child classes to define an implementation.