What you are referring to (shame on no one for noticing this, for shame) is called "method chaining". A lot of big frameworks do this. Consider this example of use:
echo $obj->setName('Mike')->convertMtoN()->getName();
// Echoes "Nike"
Cool.
But here is how it works:
class Example {
private $name = '';
public function setName($name) {
$this->name = $name;
// We return the object, so you can call it again.
return $this;
}
public function convertMtoN() {
// Let's do Caps first
$this->name = str_replace("M", "N", $this->name);
// Then lowercase
$this->name = str_replace("m", "n", $this->name);
// We return the object, keep working
return $this;
}
public function getName() {
return $this->name;
}
}
$name = new Example;
echo $name->setName('Mike')->convertMtoN()->getName();
Essentially, for each method that does not implicitly return a value, you simply return the object, allowing you to continue chaining.
Awesome, right?
PHP rocks (now, I know it has its faults, but with HHVM and process forking, it basically rocks [dude, you will get there]).
You can play with this here:
https://ideone.com/fMcQ9u
$class->send->activation_email()"send" is also a (instance of a) class not a function. If it was a function, it would be$class->send()->activation_email(), and it would have to be a function that returned an instance of a class that had a activation_email method in it.