Question

What is implementing a function? normally, what I know is implementing an interface which has

function foo(); 

and implementing like

function foo($bar)

in another class

but what happens when I implement the function in the interface? do I have to reimplement them in the subclasses? or can I use them in subclasses directly, assuming they are implemented in the subclasses.

interface ibarbar{
function foo($bar)
{ 
 return $bar.$bar;}
}

class barbar implements ibarbar
{
 function baz()
 {
 $this->barbar(); //used without implementing in subclass. expected results unknown.
 }
}

PHP documentation says

// This will not work
// Fatal error: Class BadTemplate contains 1 abstract methods
// and must therefore be declared abstract (iTemplate::getHtml)
class BadTemplate implements iTemplate
{
    private $vars = array();

    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
}

so all methods in an interface are abstract methods. but I couldn’t find how to extend a function. or implement a function

Answer 1

You can’t implement a function in an interface. You can only specify its signature.

---

If you want to specify signatures for some methods but provide implementation for others, use an abstract class:

abstract class A {
    abstract public function B($c);

    public function C($d) {
        // do something
    }
}
class B extends A {
    public function B($c) { // need to implement B, as it is abstract
        $this->C($c);       // but can directly use C, as it is not
    }
}