Welcome to hack

WELCOME TO HACK

An Introduction to the Hack Programming Language

A BIT ABOUT ME

A BIT ABOUT ME• Director of Research and

Development at Zinios.

A BIT ABOUT ME• Helped grow the PHP community

in Sydney.• Established the annual PHP

Phunconference in Sydney.

A BIT ABOUT HHVM & HACK• HHVM originally started off as HPHP.• Hip-Hop PHP.• Was released in 2009.

A BIT ABOUT HHVM & HACK• HPHP was a PHP Transpiler.• It converted PHP to C++ and then compiled that into

binary to run as highly-optimized executable machine code.

A BIT ABOUT HHVM & HACK• In 2013 Facebook released

HHVM.• Hip-Hop Virtual Machine.

A BIT ABOUT HHVM & HACK• Hack was written by

Facebook for Facebook.• Open sourced to the public

in 2015.

A BIT ABOUT HHVM & HACK• Hack is PHP, with a lot more

features.• It’s stricter.• Type orientated.• Runs on HHVM.

• Hack looks like PHP.• Often feels like PHP• But it’s not PHP.

What’s the Difference?

• Analyses source code before run time for typing errors.• Catches issues with code before they become bugs!

The Type CheckerWhat’s the Difference?

• Type Checking is performed with the hh_client program which comes with HHVM.

• It also integrates with various editors.



<?hh //strictclass App{ public function exec():void { $this->run(['bar']); } public function run(array<string,mixed> $array):void { var_dump($array); }}

Top Level Code Example

• The Type Checker gives the following error:The Type Checker


• Hack opens with a different tag.• Instead of <?php, hack opens with <?hh instead.• Hack does not permit a closing tag. ?> will cause an

error.• Hack will not process the file as a Hack file if the first 4

characters does not match the Hack opening tag.• Hack files end with the .hh extension.

What’s the Difference?Opening Tag

• Top level code is not permitted.• This is often known as procedural or objectless code.• In most situations, Hack does not permit this.

What’s the Difference?Unsupported – Top Level Code

<?hh //strictfunction foo(int $x, int $y):int{

return $x+$y;} foo(1,3);

Top Level Code Example

• The previous example will cause the type checker to throw an error.

• The method foo() was called at the top level.


• Sometimes it’s unavoidable.• Small changes make the type checker happy.



<?hh //partialfunction foo(int $x, int $y):int{

return $x+$y;}foo(1,1);

topLevel.hh

<?hh //strictrequire_once('topLevel.hh');class Bar{

public function __construct(){

foo(5,3);}

}

index.hh

• The previous example works because there is no unsupported top level code.

• The require statement is allowed.


require, require_onceinclude, include_oncenamespaceuseclass, trait, interfacefunction

• References are common practice in PHP.• Hack doesn’t permit them.• The type checker cannot do proper analysis of the

code if it uses references.• References violate the rules that the type checker

follows to properly analyze code.

What’s the Difference?Unsupported – References

• PHP’s roots are in HTML.• Mixing HTML and PHP has always been possible.• Hack doesn’t allow this.• The HHVM runtime cannot recognize files like this

when used as a Hack file (.hh).

What’s the Difference?Unsupported – HTML

• But wait...! There is a way!


• Hack also has something like React built in.• It’s called XHP and it looks something like this:


<?hh //strict$name='John Doe';print <p>Hello {$name}</p>;

XHP Example

• Some PHP intrinsic (or language constructs) are not supported in Hack.

What’s the Difference?Unsupported – Intrinsics

isset()empty()unset()

• Dynamic creation of code is not allowed.• eval and create_function are not supported.• Dynamic syntax like the following isn’t supported.

What’s the Difference?Unsupported – Dynamic Code

$this->$foo;$this->$foo();$$foo;

Unsupported Dynamic Syntax

• Variable variables.• Variable methods.• Variable properties.• All not supported because it’s impossible for the type

checker to guarantee what the results will be.

What’s the Difference?Unsupported – Dynamic Code

• PHP4 style constructors.• Template-style PHP syntax – if…endif and family.• Incrementing and Decrementing a string with ++ and --.• Word literal operators. Use “&&” instead of “and” etc.• “break x” and family are no longer allowed.• Hack is case sensitive. So if the class name is “Foo”, you

cannot instantiate it with “new foo()”.• Hack is more strict when calling methods in classes. Use

“$this”, “self” and “static” appropriately.

What’s the Difference?Unsupported – Other

• Start with Types.• Explore some other features along the way.

What’s the Difference?New Stuff

• PHP has been lacking types for a long time.• Recently introduced into PHP 7.0.• Slightly improved in PHP 7.1.• Will continue to improve.


• Type Annotations are what makes Hack so great.• They can be defined on:

– Class Properties– Method and Function Parameters– Method and Function returns– Constants– And you can type some of the new types.


WHAT’S THE DIFFERENCE?

<?phpclass DB{

public function upsert($record,$condition=[],$options=[]){

//...}

}

Basic PHP Example

• Consider the following example:

• An imaginary method.• Can insert or update a record in a database.


<?phpclass DB{

public function upsert(Array $record, Array $condition=[],$options=[]){

//...}

}

PHP 5 Example

WHAT’S THE DIFFERENCE?<?phpdeclare(strict_types=1);class DB{

public function upsert(

array $record,array $condition=[],array $options=[]

):array{

//...}

}

PHP 7.0 Example

WHAT’S THE DIFFERENCE?<?phpdeclare(strict_types=1);class DB{


array $record,array $condition=[],array $options=[]

):?array{

//...}

}

PHP 7.1 Example


<?hh //strictclass DB{


array<string,mixed> $record,array<string,mixed> $condition=[],array<string,mixed> $options=[]

):?array<string,mixed>{

//...}

}

Hack Example

WHAT’S THE DIFFERENCE?<?hh //stricttype CommonStringKeyArray=array<string,mixed>; class DB{


CommonStringKeyArray $record,CommonStringKeyArray $condition=[],CommonStringKeyArray $options=[]

):?CommonStringKeyArray{

//...}

}

Hack Aliases Example

WHAT’S THE DIFFERENCE?<?hh //stricttype CommonStringKeyArray =array<string,mixed>;type DBRecord =CommonStringKeyArray;type DBQuery =CommonStringKeyArray;type DBQueryOptions =CommonStringKeyArray;class DB{


DBRecord $record,DBQuery $condition=[],DBQueryOptions $options=[]

):?DBRecord{

//...}

}

Hack Aliasing Alias Example

WHAT’S THE DIFFERENCE?<?hh //stricttype CommonStringKeyArray =array<string,mixed>;type DBRecord =CommonStringKeyArray;type DBQuery =CommonStringKeyArray;type DBQueryOptions =shape(

'order' =>int,'limit' =>int,'offset‘ =>int

);class DB{



):?DBRecord{

//...}

}

Hack Shape Example

WHAT’S THE DIFFERENCE?<?hh //strictrequire_once('types.hh');class DB{

private ?DBConnection $connection;private bool $connected=false;private DBQuery $lastQuery;



):?DBRecord{

//...}

}

Hack Typed Properties Example

WHAT’S THE DIFFERENCE?Hack Types

boolintfloatstringarrayresource

WHAT’S THE DIFFERENCE?Hack Types

void Used for methods which don't return anything.

noreturnUsed for functions and static methods indicating that the function can never return because it either exists or throws an exception.

mixed A catch all which includes null and void.<object> Any predefined class.this For methods which return $this.num A union type of int and float.arraykey A union type of string and int.

• Most types can be prefixed with “?”.• This makes it acceptable for a method to return null in

addition to the stated type.• This does not apply to void or noreturn.• mixed already includes null.

Hack TypesWhat’s the Difference?

• Hack doesn’t allow the “callable” type in strict mode.• Instead, you need to express the shape of the callable.



function send(

Map<arraykey,mixed> $payload,(function(Map<arraykey,mixed>):bool) $callback

):this{

//...}

Callable Example

• Hack supports Tuples.• Tuples are considered as arrays.• But they have restrictions.


• Tuples have a fixed size and fixed types.• Values may be changed. But must be the same type.


function findFirst(array<string> $arr, string $likeRegex):(string, int){

//...}

Tuple Example

• Enum is another type supported by hack.Hack Types


enum Size:int{

SMALL =0;MEDIUM =1;LARGE =2;XLARGE =3;

}

Enum Example

• Collections are provided to as specialized classes.• They implement specific container patterns.• Almost always better to use.• Better optimization results from HHVM.

CollectionsWhat’s the Difference?

• Hack provides 4 types of collections.Collections


MapVectorSetPair

• A collection of values with strings or integers as index keys.

• This collection is the most similar in functionality to when comparing with a PHP array.

Collections – MapWhat’s the Difference?

• A collection of values which only supports integer indexed keys.

Collections – VectorWhat’s the Difference?

• A special collection.• It is keyless.• It only supports strings and integers as values.

Collections – SetWhat’s the Difference?

• Another special collection.• It only supports 2 values.• It has 2 indexed keys – 0 and 1.• It is immutable.

Collections – PairWhat’s the Difference?

• Each type of collection has an immutable counterpart.• Except Pair because it is already immutable.

Collections – ImmutablesWhat’s the Difference?

ImmMapImmVectorImmSet

• Each type of collection has a literal syntax that can be used in place of “new X()”.

Collections – Literal SyntaxWhat’s the Difference?

Map{'foo'=>1,'bar'=>2};Vector{1,2,3}Set{'a',1,'b',2}Pair{0.21455657,123.25366212}

Literal Collection Syntax

• Attributes• Allow you to apply metadata to things like classes and

methods.• This is reflectable.

Many Other New FeaturesWhat’s the Difference?


<<command('encryptString'),arguments(

[['--input','-i'],'The string to encrypt.'

])

>>public function encryptString(Command $command){}

Attributes

• Pipe Operator• The Pipe operator allows for a more concise, fluid,

syntax for chaining together expressions.


$path=implode('/',explode('\\',$this->getPath()));

The Old Way

$path =$this->getPath()|>explode('\\',$$)|>implode('/',$$);

The New Way

• Null Safe Operator: $x?->foo() • Constructor Promotion• Trait and Interface Requirements• Cooperative Multitasking with Async• Lambdas and Lambda Operator: ==>• And many more…


PITFALLS• Some tips to help you avoid common traps.• Remember that this is not PHP.• In many ways it looks like PHP, but its behaviour can

be very different.

PITFALLS• Always use the type checker.• It’s not an accessory which you boot up sometimes.• It’s your pre-emptive strike against the infectious bug

overlords.

PITFALLS• Don’t try and trick the type checker!• This === Dragons

PITFALLS• PHP allows for some very dynamic code.• It’s very forgiving.• HHVM does not allow this and trying to trick the type

checker can cause unforeseen behaviours in your code.

PITFALLS• Sometimes HHVM forgives.• This leads to head scratching moments.• It works! But… wait what???• Side effects can be caused by

bad code.• Mostly happens when the type checker is used incorrectly or not

at all.• Sometimes it’s a bug in HHVM.

PITFALLS• Partial mode is NOT your friend.• Don’t write your code against partial mode.• There are many benefits to writing strict Hack.

PITFALLS• HHVM will run PHP code with Hack code and Hack

code with PHP code.• Great for code migration.• Bad for achieving a 100% strict codebase.

PITFALLS• Sometimes you’ll be developing against a third party

library.• It could be from composer (Yes, everything from

composer will run on HHVM!)• In this case, you can use a HHI definition file to explain

to the type checker, all the methods and types which come from those libraries.

• Can use pre-baked Images or bake scriptsInstallation

Getting Started with HHVM & Hack

• Manual installation is simple with pre-built packages.• Ubuntu is as simple as “sudo apt-get install

hhvm”.• Alternatively build from source.

– https://github.com/facebook/hhvm

InstallationGetting Started with HHVM & Hack

• Read The Manual!– http://docs.hhvm.com/ - Everything you need in one place.

• A great series on getting started available on Engine Yard.– https://blog.engineyard.com/2014/hhvm-hack

LearningGetting Started with HHVM & Hack

• Not many pure Hack frameworks.• Community is still growing.

Use a FrameworkGetting Started with HHVM & Hack

• Zinios is one company trying to help.• We’re releasing the core of our application platform.


• Nuclio is fully open source and will be available soon.• You can request early access from me!• http://nuclio.co


THANK YOU!

Internet

Welcome to hack