Hack is a programming language designed for the HHVM runtime. HHVM compiles PHP and Hack code into an intermediate bytecode which is then JIT compiled to machine code, providing better performance than traditional PHP execution. Some key features of Hack include gradual typing, generics, and async functions. Hack brings together popular features from PHP, C#, and Java. Facebook uses HHVM and Hack to realize a 9x increase in request throughput and 5x reduction in memory usage compared to traditional PHP.

1. Hack & HHVM
by
EWERE DIAGBOYA

2. Table of Contents
- What is Hack ?
- What is HHVM?
- Installing HHVM
- Some Statistics on HHVM
- Features of Hack
- Code Comparison/Similarity
- Who is using HHVM
- Pros and Cons
- Conclusion
- Demo

3. What is Hack
Hack is a programming language for HHVM. Hack reconciles the
fast development cycle of a dynamically typed language with
the discipline provided by static typing, while many features
commonly found in other modern languages.
Hack was inspired by PHP, C# and Java so it brings the features
of these languages together into itself to form a single language
with syntax very close to PHP (developed by Facebook)

4. What is HHVM
HipHop Virtual Machine (HHVM) is a process virtual machine
based on just-in-time (JIT) compilation, serving as an execution
engine for PHP and Hack programming languages.
By using the principle of JIT compilation, executed PHP or Hack
code is first transformed into intermediate HipHop bytecode
(HHBC), which is then dynamically translated into the x86-64
machine code, optimized and natively executed (developed by
Facebook)

5. HHVM In Summary
Rather than directly interpret or compile PHP code directly to
C++, HHVM compiles Hack and PHP into an intermediate
bytecode. This bytecode is then translated into x64 machine
code dynamically at runtime by a just-in-time (JIT) compiler.
This compilation process allows for all sorts of optimizations
that cannot be made in a statically compiled binary, thus
enabling higher performance of your Hack and PHP programs.

6. NB: It actually takes a while to compile the code on HHVM but once compiled it can then run faster
and has cache for storing unchanged files to enable it run faster

7. Installing HHVM
HHVM has Linux ready distros to be deployed on Ubuntu
and others. It is quite easy to install. But HHVM does not
work on all its own, it is configured either on Nginx or
Apache Server

8. Some Statistics

9. Statistics
According to Facebook, HHVM has realized over a 9x increase in web
request throughput and over a 5x reduction in memory consumption
for Facebook compared with the Zend PHP engine + APC (which is the
current way of hosting a large majority of PHP applications).

10. Source: OSCON

11. Source: OSCON

12. Some Features of Hack
- Gradual Typing (Static and Dynamic Typing) *
- Collections (Vectors, Set, Map, StableMap)
- Generics *
- Async Functions *
- Lambda Expression

13. Gradual Typing in Hack
Hack has a unique typing system where the user can
choose to use strict typing or decide not to use typing at
all, which makes it similar to its influencer PHP.
But Facebook warns that to get the full power of HHVM
strict typing is recommended

14. Gradual Typing in Hack
<?php
string $name = “This is PHP”;
PHP Code
<?hh
string $name = “I am learning Hack”;
Hack Code
Sample Code
Data Types supported in Hack include: bool, int, float, num, string

15. Generics
Generic programming is a style of computer programming
in which algorithms are written in terms of typesto-be-
specified-later that are then instantiated when needed for
specific types provided as parameters.
In simple terms it allows classes and methods to be
parameterized (i.e. a type associated when a class is
instantiated or a method is called

16. Generics (Sample Code)
<?hh
class Box<T> {
protected T $data;
public function __construct(T $data) {
$this->data = $data;
}
public function getData(): T {
return $this->data;
}
}
Hack Code

17. Async Functions
Asynchronous programming refers to a programming
design pattern that allows several distinct tasks to
cooperatively transfer control to one another on a given
thread of execution.
The tasks are isolated from one another from the
perspective of dependency minimization and task
interaction. Asynchronous programming is most often used
in the context of input/output (I/O)
Allow multiple functions to run cooperatively

18. Async Functions (Sample Code)
<?hh
async function getPage($url) :
Awaitable<string> {
sfp = fopen($url, ‘r’);
return await async_get_contents($fp);
}
// Sends all requests in parallel,
// blocks for response
$pages = await (
getPage(‘http://php.net’),
getpage(‘http://example.com’),
getPage(‘http://hhvm.com’),
);
Hack Code

19. Comparison & Similarity
<?hh
class MyClass {
public function alpha(): int {
return 1;
}
public function beta(): string {
return 'hi test';
}
}
function f(MyClass $my_inst): string {
return $my_inst->beta();
}
Hack Code
<?php
class MyClass {
public function alpha() {
return 1
}
public function beta() {
return ‘hi test’;
}
function f() {
return $this->beta();
}
PHP Code

20. Who is using HHVM ?

21. Advantages of Hack & HHVM
- More Features in Hack than PHP
- Runs faster than PHP
- Higher general perform and less resource usage
- Compatible with alot of CMS and Frameworks
(Magento, CodeIgniter, CakePHP, Laravel etc)
- Compiles to a more efficient native code
- Only recompiles when changes are made to a file

22. Disadvantages of Hack & HHVM
- Compile Time might be high
- Learning a new syntax might take a while
- Incompatibility issues with PHP & HHVM
- Facebook could stop support for Hack & HHVM which
could slow down its growth
- Does not allow direct HTML in its code

23. Conclusion
PHP is an old language and very dear to alot of us but
Hack and HHVM show us better ways to improve our code
and build features that do not currently exist on PHP, and
give the performance PHP is yet to give.
The final option might be to run good old PHP on HHVM
and still get good performance or learn Hack and use the
new tools it presents. Either way the goal is to increase
performance with less resources and give the user a
better experience of the application

24. Demo
Simple POST in Hack

25. Thank you
Further Reading
www.hacklang.org
www.hhvm.com
www.github.com/facebook/hhvm
www.github.com/hhvm