Hack is a programming language developed by Facebook in 2014. It was designed to interoperate with PHP and to address some of the challenges that developers faced while working with PHP at scale. Hack was created by Julien Verlaguet, along with others on the Facebook engineering team, to improve the reliability, maintainability, and performance of their codebase without abandoning the familiar syntax and ecosystem of PHP. By introducing Hack, Facebook aimed to strike a balance between dynamic and static typing, offering the flexibility of PHP while providing the benefits of a type system for better error detection and efficiency.
One of Hack’s key features is its support for gradual typing, which allows developers to combine both dynamically and statically typed code within the same program. This means that developers can choose when and where to enforce strict typing, giving them more control over the development process. It also helps catch errors early, at compile time, rather than at runtime, which is a common issue in dynamically typed languages like PHP.
Hack introduced a type checker called HHVM (HipHop Virtual Machine), which acts as a runtime environment and allows the code to be executed faster than traditional PHP, due to its just-in-time (JIT) compilation capabilities. This performance boost made Hack an attractive option for developers, particularly those working with large codebases like Facebook’s.
In addition to its typing system, Hack also brings in modern programming features such as generics, collections, lambda expressions, and async/await for handling asynchronous operations. These features make Hack a more powerful and expressive language, suitable for building high-performance, scalable applications.
An example of a simple Hack program that prints "Hello, World!" looks like this:
<?hh
function main(): void {
echo "Hello, World!";
}In this code, the : void type declaration after main() indicates that the function does not return a value. The syntax is similar to PHP, making it accessible to developers familiar with that language while still providing the benefits of static typing and other modern features.
Hack is widely used within Facebook for maintaining their massive codebase. The ability to gradually adopt type-checking allowed the company to evolve its PHP code incrementally, improving safety and performance without needing a complete rewrite. Outside of Facebook, Hack has been used by developers who appreciate its blend of type safety and dynamic capabilities, especially in large-scale web development projects where performance and reliability are critical.
Overall, Hack provides a good balance between ease of use and powerful, modern programming paradigms, making it an excellent choice for developers transitioning from PHP or working on complex systems. It offers the flexibility of dynamic typing when needed, alongside the reliability and maintainability of static types, all while boosting performance with its JIT compilation through HHVM.