Interface

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are implemented.

Interfaces may have methods signatures, without a body, and constants.

<?php

// Declare the interface 'Template'
interface Template
{
    public function setVariable($name, $var);
    public function getHtml($template);
}

// Implement the interface
// This will work
class WorkingTemplate implements Template
{
    private $vars = [];

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

    public function getHtml($template)
    {
        foreach($this->vars as $name => $value) {
            $template = str_replace('{' . $name . '}', $value, $template);
        }

        return $template;
    }
}

?>

Documentation

See also Interfaces vs Abstract Classes in PHP, Interfaces - the misunderstood concept, Granular interfaces, When to add an interface to a class, Code to an interface!

Related : Fluent Interface