MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Stories from
the Other Side
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Exploring OOP and
Functional Programming
(to become a better programmer)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Why am I interested in this?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Smart guys go FP (lambdalicious, phunkie)
The Little Schemer
Scala is the rage!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What is this, OOP + FP?
Where did these paradigms start?
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The term "Object Oriented Programming"
was coined by Alan Kay
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Original image by Marcin Wichary - Thanks!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Amongst many other achievements,
Alan Kay created Smalltalk
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

"OOP to me means only messaging,
local retention and protection
and hiding of state-process,
and extreme late-binding of all things"
It can be done in Smalltalk and in LISP."
~ Alan Kay
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

"It can be done in Smalltalk and in LISP."
wait... WHAT?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

OOP in LISP?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

((lambda (f)
(define pick
(lambda (n lat)
(cond
((zero? (sub1 n)) (car lat))
(else (pick (sub1 n) (cdr lat))))))
It's lists and recursion all the way down
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

How does OOP work with that?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What is OOP?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Is it about inheritance?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

"OOP to me means only messaging,
local retention and protection
and hiding of state-process,
and extreme late-binding of all things"
~ Alan Kay
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Kay doesn't mention inheritance.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Is OOP about classes?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Kay doesn't mention classes either.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

If OOP is not about
classes or inheritance,
what is it about?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Lets start with
Messaging
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

I guess that means method calls.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

In class based OOP,
the methods of a class define its
Interface.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Interface
==
Related Methods
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Quite similar to
related Functions
within a Namespace
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So OOP is about grouping methods together?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

"... local retention and protection ..."
~ Alan Kay
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Oh yeah, objects have states.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What is a state?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

State in class based OOP:
class Foo
{
private static $class_state = 42;
private $instance_state = -0.2;
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

State in RL is more like
public function __construct(...)
{
$this->type = 'simple';
$this->customerSession = $customerSession;
$this->scopeConfig = $scopeConfig;
$this->counter = 0;
$this->id = $_REQUEST['id'];
$this->names = $db->getNames();
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What properties do these examples of
state have?
public function __construct(...)
{
$this->type = 'simple';
$this->customerSession = $customerSession;
$this->scopeConfig = $scopeConfig;
$this->counter = 0;
$this->id = $_REQUEST['id'];
$this->names = $db->getNames();
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

A literal
$this->type = 'simple';
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

A shared object
$this->customerSession = $customerSession;
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Literal zero
(but looks like that might change)
$this->counter = 0;
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Global state
$this->id = $_REQUEST['id'];
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Stuff from the DB
$this->names = $db->getNames();
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Can we partition those examples?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

1. State that is always the same
2. State that might change
(within the lifespan of the object)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

State that might change:
→ Counter
→ Session
→ Filesystem / DB / Internet
→ Globals
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Non-changing state
→ The Type ID
→ Application State
→ Configuration
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What can we do with
this information?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Pure
Functions!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Pure functions?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Don't cause any side effects
→ Given the same arguments
always return the same result
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

What are
side effects?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Changing state non-local to the
function scope
→ DB or Filesystem or Network access
→ Throwing Exceptions
→ Forking
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

No side effects
was one part.
What was the other?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Same Arguments
==>
Same Result
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A function that always returns the same
result given the same arguments is called
Referentially Transparent
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Referentially Transparent Functions
must not use state that might change!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Why should we care?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Benefits
of Pure Functions!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Easier to think about
(reasonability)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Easier to break apart
(decomposability)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Easier to combine
(composability & reuseability)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Easier to show correctness
(testability)
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

→ Easier to parallelize
(threadability ;))
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Mkay.
But what about the
changing things?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

How can we deal with changing state?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We treat objects as snapshots of the
state of the world in one moment.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

The state of the world in that
moment will never change.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

If change occurs, it means now is a
different moment in time.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We can represent change in two ways:
→ by modifying the object
→ by creating a new instance
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Immutability
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For example, what happens when an
admin logs in?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

$loggedInAdmin = $loggedOutAdmin->login();
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

public function login()
{
return new self($isLoggedIn = true);
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

But what if a method
needs the
"current instance"?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Either that object has to be recreated
with the current instance,
or the current instance has to be
passed as a method argument.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

OOP style
$authorizationManager->hasAccess($dashboard, $loggedInAdmin);
$authorizationManager->hasAccess($dashboard, $loggedOutAdmin);
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

In FP
$has_access($dashboard, $loggedInAdmin);
$has_access($dashboard, $loggedOutAdmin);
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

There are more
parameters in RL!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Okay, lets reduce the argument count by
adding properties to the object.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

$dashboardAuthorizationManager =
new class($authorizationManager, $dashboard) {
private $authorizationManager; private $page;
public function __construct($authorizationManager, $page)
{
$this->authorizationManager = $authorizationManager;
$this->page = $page;
}
public function hasAccess($admin)
{
return $this->authorizationManager
->hasAccess($this->page, $admin);
}
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Only one argument left:
$pageAuthorizationManager->hasAccess($loggedInAdmin);
$pageAuthorizationManager->hasAccess($loggedOutAdmin);
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

How might that look like in FP?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

$has_access_to_dashboard =
function ($admin) use ($dashboard, $has_access) {
return $has_access($dashboard, $admin);
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

$has_access_to_dashboard($loggedInAdmin);
$has_access_to_dashboard($loggedOutAdmin);
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Can we remove all
arguments?
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

$loggedInAdminDashboardAuthorization =
new class($dashboardAuthorizationManager, $loggedInAdmin)
{
private $pageAuthorizationManager; private $admin;
public function __construct($pageAuthorizationManager, $admin)
{
$this->pageAuthorizationManager = $pageAuthorizationManager;
$this->admin = $admin;
}
public function hasAccess()
{
return $this->pageAuthorizationManager
->hasAccess($this->admin);
}
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

In FP:
$has_logged_in_admin_access_to_dashboard =
function () use ($has_access_to_dashboard, $admin) {
return $has_access_to_dashboard($admin);
}
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We can bundle state
and functions
without classes!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We can bundle state
and process
without classes!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Look Ma,
OOP in PHP without
hands classes!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We have the choice:
→ pass state with method arguments
→ set state as object properties
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

The more volatile the object state,
the more often we need to
create new instances...
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

...if we want to have
Pure Functions.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Lesson from FP:
Distinguish between mutable and
immutable object properties.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

"Mutable stateful objects are the new
spaghetti code"
~ Rich Hickey
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Summary
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Concepts from the FP languages can be
useful in OO PHP.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We can benefit from designing our
OO code so it exhibits the properties of
pure functions.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

We barely scratched the surface.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Don't be afraid of FP's mathematical
pattern names. It's still just code.
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

Building these slides I
learned something about OOP.
I hope you found it interesting, too!
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp

(if (has-communication? you vinai)
(communicate you vinai)
(enjoy you remaining-agenda))
MageTitans Manchester, UK - #MageTitansMCR 2016-11-12 - twitter://@VinaiKopp