This document summarizes a presentation given on why to choose Hack/HHVM over PHP7. Some key points made include: 1. Hack provides more powerful type hinting capabilities compared to PHP7, including support for nullable and mixed types. 2. Hack features original collections like Vector, Map, Set and Pair that allow specifying value types, unlike PHP arrays. 3. Hack has original language specifications like lambdas, generics, and enums not in PHP7. 4. Hack allows parallel execution out of the box for higher performance. 5. Hack's static analysis tool catches errors before runtime for more bug-free code. 6. HHVM continues to incorporate features from PHP

1. Why choose Hack/HHVM
over PHP7
Intelligence, Ltd.
Yuji Otani
1
Presented on Feb 24, 2016

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• Born in Shimonoseki, Yamaguchi Prefecture
• Software Engineer at Intelligence, Ltd
• I love cars and programming
• Be my friend on Facebook!
https://www.facebook.com/yuji.otani.16
About me:

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5years
→ →
My main experiences with
programming languages:
7years
1year

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Question 1
Have you used
Hack/HHVM?

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Question 2
PHP7 has been released.
Are you uncertain about
what to use next?

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Goal of this presentation:
Convey the qualities of Hack/HHVM
and make you consider it

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We have adopted Hack/HHVM in many
projects here at Intelligence since 2015.
The Framework of our choice is FuelPHP.

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Example: MIIDAS (job hunting service)
https://miidas.jp

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Example: MyRefer (employee referral service)
https://i-myrefer.jp/

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• a programming language developed by Facebook
• compatible with PHP
• runs on HHVM (virtual machine)
• based on PHP5.6
What is Hack?

11. • bug-free and fast coding
• enjoyable coding experience
• fast runtime
• fit for large scale systems
The goals of Hack:
http://growthhackjapan.com/2014-03-23-facebook-hack-released-to-the-public/

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• we wanted to challenge something new while
leveraging the experience with PHP
• we wanted to deliver a performant service
• we wanted to keep the ease of readability and
maintainability even when the system grew bigger
• PHP7 was not available yet
Why we chose Hack:

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At the end of last year, the big
happening

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Dec 3, 2015
PHP7 was released!

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Huge performance improvements!!
http://talks.php.net/fluent15#/wpbench

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• Null coalesce operator
• EngineException (catchable fatal errors)
• anonymous classes
• scalar type hinting
• return type declaration
New language specifications

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• optimized for 64-bit CPUs
• efficient use of CPU cache
• in-memory arrays became sequences (in PHP5 they were all
associative arrays)
• the memory usage by arrays has improved dramatically.
* PHP5 (72bytes) → PHP7 (32bytes)
New data structure

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PHP7 incorporated many features
from Hack/HHVM
• scalar type hinting
• return value declaration
• great performance
• lower consumption of memory for arrays
• AST (abstract syntax tree) compiling

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Currently PHP faces a big turning point.
That's precisely the reason why I want you to
know the qualities of Hack/HHVM.

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Point 1
Powerful type hinting

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What is type hinting?
You can specify the type of arguments and return values of
functions.
Class Sample {
public static function sampleFunc(int $a): string{
return "OK";
}
}
//OK
Sample::sampleFunc (1);
//Fatal Error
Sample::sampleFunc ("a");

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Type hinting in PHP
Types that could be used in type hinting were gradually added.
PHP5.0 ：Class
PHP5.1 ：array
PHP5.4 ：Closure and function
PHP7 ：Scalar Type (int, float, string, bool)

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There are major differences in type
hinting between Hack and PHP7

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PHP7 type hinting
There are 2 modes:
• Weakly typed = automatic type casting
• Strongly typed = strict type checking
<?php
Class Sample {
public static function sampleFunc(int $a): string{
return "OK";
}
}
// OK in both modes
Sample::sampleFunc(1);
// OK only in weakly typed mode
Sample::sampleFunc("1");

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PHP7 type hinting
• The default mode is “weakly typed”
• To switch to “strongly typed” mode, it is necessary to
declare it in the beginning of the source files
• It’s only possible to declare “strongly typed” mode per file,
i.e. it’s not possible to declare “strongly typed” mode in
configuration files
<?php
// "Strongly typed" mode is enabled in this file only
declare(strict_types=1);

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PHP7 type hinting
• It is not possible to declare nullable or mixed types.
• Passing Null to a function with type-hinted parameters will
trigger error.
<?php
Class Sample {
public static function sampleFunc(int $a): string{
return "OK";
}
}
//Fatal Error
Sample::sampleFunc(null);

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Hack type hinting
• Only “strongly typed” mode
• Permits any type (including null) by using the “mixed”
keyword
<?hh
Class Sample {
public static function sampleFunc(mixed $a): string{
return "OK";
}
}
//OK
Sample::sampleFunc(null);
Sample::sampleFunc(1);
Sample::sampleFunc(”a");

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Hack Type Hinting
• Accepts Null by adding a “?” before the type hint
<?hh
Class Sample {
public static function sampleFunc(?int $a): string{
return "OK";
}
}
//OK
Sample::sampleFunc(null);
Sample::sampleFunc(1);

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Hack Type Hinting
The types of keys and values of arrays can be specified.
However, it is only for static analysis, not runtime.
<?hh
Class Sample {
public static function sampleFunc(array<int, string> $a): string{
return "OK";
}
}
//OK
Sample::sampleFunc(array(1 => "a", 2 => "b"));
Sample::sampleFunc(array(1 => 1, 2 => null));

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Hack Type Hinting
It is possible to specify types in Enum.
<?hh
enum Size: int {
MEDIUM = 1;
LARGE = 2;
}
Class Sample {
public static function sampleFunc(Size $size): string{
return "OK";
}
}
//OK
Sample::sampleFunc(Size::LARGE);
Sample::sampleFunc(2);
Sample::sampleFunc(4); // This works too: it checks the type, not the value.
//Error
Sample::sampleFunc(”a");

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Type Hinting
• “Strongly typed” only
• Nullable and mixed types
The specifications put emphasis on
type-sensitive, large scale systems.
• “Weakly typed” by default
• No nullable nor mixed types
The specifications put emphasis on
the speed of type-agnostic
development.

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Point 2
Collections

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PHP5 arrays:
• Arrays and associative arrays can be used in the same way
• Arrays accept values of any type
• Keys can be integer or string
• Values are retrieved in order of insertion, regardless of keys
<?php
// the code below prints “ab”
$arr = array(1 => ”a", 0 => ”b");
foreach($arr as $value ) {
print($value);
}

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Hack Collections:
• Has original collections: Vector, Map, Set and Pair
• It is possible to specify the types of keys and values, though
they’re not checked during runtime
<?hh
$a = new Map<string, string>;
//OK
$a->set("key1", "value1");
//OK
$a->set("key2", 2);
//OK
$a->set(3, array());

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Hack Collection
It’s not necessary to check if the key exists prior to fetching a
value, and it won’t trigger a “Notice” error when the key doesn’t
exist.
<?hh
$a = new Map<string, string>;
$a->set("key1", "value1");
// $val1 becomes “value1”
$val1 = $a->get("key1");
// $val2 becomes null, no “Notice” error fired
$val2 = $a->get("key2");

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Map
Stores key-value pairs
B
A
D
EC

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Vector
Pure stack-like ordered array
21 4 53

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Set
Ordered collection of unique values
BA D EC

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Pair
Immutable collection of exactly 2 values

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Collection
• Four original collections
• It is possible to specify the types
of values (keys as well for Maps)
The specifications put emphasis on
type-sensitive, large scale systems.
• Only arrays that accept any type
• No concern over the types of
arrays and their values
The specifications put emphasis on
the speed of “anything-goes”
associative arrays.

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Point 3
Original specifications

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Original features:
• Lambdas
• Generics
• Enum
• Tuples
• Shapes

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Enum (Enumeration of value)
<?hh
enum Size: int {
SMALL = 0;
MEDIUM = 1;
LARGE = 2;
X_LARGE = 3;
}
Enumerate values with a specific type

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Tuples
<?hh
list($a, $b) = testFunc();
public function testFunc() : (string, int) {
return tuple(“OK”, 1);
}
Return multiple values ​​from a function

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Original language specification
Hack/HHVM has added many original language specifications.
By using Hack in your service, you can achieve:
• quick development with fewer bugs
• developers actually enjoy coding

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Point 4
Parallel execution

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Parallel execution
It is possible to run statements in parallel by using
original functions such as “Async” and “Await.”
Parallel execution is possible out-of-the-box,
reaching even higher performance speeds.

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Parallel execution

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Point 5
Static analysis tool

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Static analysis tool
The static analysis of the code is done by hh_client. It
checks for syntax errors and inconsistencies, allowing
developers to fix them before runtime.
Code with fewer bugs like this is only possible due to the
strict type restrictions in Hack.

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You can check the program before execution.
• Check for compilation errors
• Type-check the arguments and return values
• Check for discouraged syntax
• Check for inappropriate type casting
Static analysis tool
* configure automatic static analysis with hhvm.hack.lang.auto_typecheck
in config files.

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Point 6
Gradually adopting features from PHP7

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Continued support for both PHP5 and 7
• HHVM3.11 implements the new features in PHP7
• The direction is to support both PHP5 and PHP7
• Also possible to break backward compatibility by setting
“hhvm.php7.all = 1” in the settings
• Features from PHP7 can be individually enabled
https://docs.hhvm.com/hhvm/configuration/INI-settings#php-7-settings

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Point 7
Great adoption record

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Great adoption record
The adoption continues to grow, especially among large
scale services. Wikipedia and Baidu have many commits into
the source code to Hack/HHVM.
https://github.com/facebook/hhvm/wiki/Users

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Although Hack/HHVM is very nice,
there are also unfavorable qualities

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Release cycle
Hack (HHVM)
• Released every 8 weeks
• Every 3rd version is turned into the LTS version, which is
supported for one year
PHP
• Released every 1 year
• Life cycle of 3 years (bug fixes 2 years, security 1 year)

58. LTS are supported for about 1 year
Hack/HHVM support

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• HHVM crash: needed to monitor to restart
automatically
• pecl not supported: tried replacing some with
golang, but currently venturing into HNI
• Had to upgrade CentOS6 to CentOS7 due to
sudden end of support
• Most of IDEs don’t support it
Some issues we faced in production

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Hard to find resources
Problem

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PHP7 support in HHVM

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PHP7 support in HHVM
http://hhvm.com/blog/10859/php-7-support

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TLDR;
• The release of PHP7 is also fortunate to HHVM
• New features in PHP7 will be available from HHVM3.11
• HHVM will continue supporting both PHP5 and PHP7
• Possible to break backward compatibility by setting
“hhvm.php7.all = 1” in the settings
https://docs.hhvm.com/hhvm/configuration/INI-settings#php-7-settings

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Issues related to PHP7 can be tracked on GitHub
https://github.com/facebook/hhvm/labels/php7%20incompatibility

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Wrap-up
• PHP7 and Hack are similar, but with different
features
• Hack seems to more suited to large scale systems
• Hack didn’t split from PHP, it synchronizes and
evolves together

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PHP specifications are community-driven, while Hack
is mainly developed by Facebook.
I think PHP values the “loose PHP-ness,” while Hack
values the “correct practical use.”
Final thoughts

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It is great to have options in the future of
an excellent language like PHP!

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PHP7 is out, but it is still worth to
choose Hack/HHVM!

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thank you

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This document was created with accuracy in mind, but
the author does not guarantee its veracity nor its
usefulness. In addition, this material was created solely
by the author, and it does not represent the views,
values, etc. of any organization.
Disclaimer