Inheritance

So far we've described how to make a PHP class, constructors, destructors, and cloning.
We've said unlike the default copy-on-write semantics of array assignment, object assignment in PHP is by reference. Let's now turn to inheritance.
Inheritance in PHP is very similar to Java.
A PHP class can extend one other class.
```
class A{}
class B extends A {}
```

PHP also has a notion of interface:

interface MyInterface
{
    function method1($a, $b);
}

A PHP class can implement multiple interfaces:

class C implements MyInterfaceA, MyInterfaceB {}

If you want to have a class with some but not all of its methods defined. You can use the keyword abstract on those methods which will be overriden in subclasses.

Referring to Parents, Final

Consider:

class A {function foo(){} }
class B extends A {function foo(){} }

Within B, self::foo() refers to the redefinition of foo given in the second line above. (Instance methods can also be called using $this->method())
Within B, parent::foo() refers to class A's version of foo.
To prevent a function from being overridden in a subclass you can use the keyword final.
```
class A {final function foo() {} /* can't override*/ }
```

Namespaces

Like C++, PHP supports a notion of namespace. This is similar to the Java notion of package. It allows one to group together a collection of functions, constants, classes, interfaces under one name.
Namespaces must be declared at the start of the file they are in (only the declare command can occur earlier)
A namespace might be declared with a line like:
```
namespace TheNameOfMyNamespace;
// code for namespace
class A
{
  //code for class A
}
function foo()
{
}
```
This declaration with the same name can be at the top of multiple files if you would like to group the contents of these files into the same namespace.
A sub-namespace of a namespace can be declared using backslashes:
```
namespace TheNameOfMyNamespace\MySubNameSpace;
//code
```
Within one file you can switch what namespace you are defining, but it is not recommended:
```
namespace D {
  // code for D
}
namespace E {
  // code for E
}
```

Using Namespaces

Function or class names without qualifications are assumed to come from the current namespace:
```
namespace N;
function foo()
{
  //some code
}

foo(); //assume N namespace.
```

Before function, interface, class, or constant names we can also give the namespace path (either relative or absolute):

M\foo(); /*in context of above we are in N namespace already, 
          so M\foo() means the foo() in N\M namespace. */
\N\M\foo();
\time(); //time function in the global (default) namespace.

You can import a namespace using the use keyword:

use A\B\C;
//rather that type $a= new A\B\C(); you can type $a= new C();
use D\E\F as G;
//rather than typing D\E\F\goo(); could type G\goo();

Let's Build Something

Download the following project:
email_validator.zip
Add code to the EmailController class so that it does was is specified in the comments there as well as the comments in EmailView.php
Post your version of this class to the Mar 9 Discussion Thread.

Traits

Traits are a PHP language feature added in PHP 5.4, probably deriving from Python/Common Lisp mix-ins.

They allow one to define a collection of method implementations and then reuse them in several classes:

trait MyMethods 
{
    function getFoo() { /* code for getFoo */ }
    function getGoo() { /* code for getFoo */ }
}

class SomeClassA extends NeedsMethods 
{
    use MyMethods; //as if I had written the code in MyMethods here
    /* rest of SomeClassA code */
}

class SomeClassB extends NeedsMethods 
{
    use MyMethods;
    /* rest of SomeClassB code */
}

$a = new SomeClassA();
$a->getFoo();

You can import more that one trait by comma separating them:
```
class A  
{
   use MyMethodsA, MyMethodsB;
   // ...
}
```
Suppose both MyMethodsA and MyMethodsB define a function named foo and one named goo. This will result in a fatal error unless one explicitly resolves the conflict using the insteadof operation to say which to use, or uses the as operator to rename one:
```
use MyMethodsA, MyMethodsB {
    MyMethodsA::foo insteadof MyMethodsB;
    MyMethodsB::goo insteadof MyMethodsA;
    MyMethodsA::goo as gooey;
    MyMethodsB::foo as protected fooey; //notice can change visibility if want
}
```

Exceptions

PHP supports try catch blocks like Java.

try {} catch(MyException $e){} catch(Exception $ee){}

You can use the keyword throw to throw an exception

if($denom == 0){
    throw new Exception("divide by zero");
}

You can subclass Exception to create custom exceptions.

Namespaces, Traits, Exceptions

Outline

Cloning