Learn HACK with Real Code Examples

Hack combines dynamic typing of PHP with optional static typing.

It allows gradual typing, meaning developers can mix typed and untyped code.

Designed for web development at scale, particularly within the Facebook ecosystem.

Gradual typing system

Async programming with awaitables

Generics and type annotations

Shape types for structured data

Hack collections (vec, dict, keyset)

Gradual typing (dynamic + static)

Collections (vec, dict, keyset)

Async programming with awaitables

Functions, classes, and traits

Shapes and generics for structured data

src/ - main Hack codebase

lib/ - reusable libraries

tests/ - unit and integration tests

docs/ - project documentation

configs/ - HHVM and server configurations

Write Hack code with optional types

Run using HHVM interpreter or server

Test functions, classes, and async tasks

Compile or run scripts for production

Integrate with PHP code if necessary

Beginner: small Hack scripts and functions

Intermediate: collections and async functions

Advanced: generics, shapes, and type-safe code

Expert: large-scale web application architecture

Migration: PHP to Hack gradual typing adoption

Adds static typing to PHP

Runs on HHVM instead of standard PHP engine

Better for large-scale web applications

Supports async and modern language features

Smaller ecosystem than mainstream PHP

2014 – Hack created by Facebook

2015 – HHVM integration stabilized

2016 – Async programming and collections introduced

2018 – Generics, shapes, and typechecker improvements

2020s – Ongoing maintenance and ecosystem updates

Gradual typing: mix of static and dynamic types

HHVM: HipHop Virtual Machine for Hack/PHP

Collections: vec, dict, keyset types

Awaitable: async result to be awaited

Shape: structured data type with fixed fields