Hack (Meta) Questions and Answers for Viva

Answer-1: Hack is a programming language for the HipHop Virtual Machine (HHVM), developed by Meta (formerly Facebook).

Answer-2: Hack was introduced in 2014.

Answer-3: Hack is designed for high-performance, type-safe web development, combining static typing with dynamic features.

Answer-4: Hack is a programming language built on top of PHP, and most PHP code runs in Hack with minimal modification.

Answer-5: Static typing means that variable types are known and checked at compile time rather than runtime.

Answer-6: The Hack type checker (hh_client) ensures type safety and catches errors before execution.

Answer-7: Hack Collections are specialized data structures like Vector, Map, Set, which provide better performance and type safety.

Answer-8: Key features include gradual typing, async programming, collections, and lambda functions.

Answer-9: Gradual typing allows mixing statically typed and dynamically typed code in the same program.

Answer-10: A variable is declared with a $ prefix, e.g., $var = 10;.

Answer-11: Functions in Hack are declared using the function keyword, followed by a name and parameter list.

Answer-12: Type annotations specify the type of variables, function parameters, and return values, e.g., function add(int $a, int $b): int { return $a + $b; }.

Answer-13: Awaitable represents a value that will be available in the future, used in asynchronous programming.

Answer-14: The async keyword defines functions or blocks that execute asynchronously.

Answer-15: await is used to pause execution until an Awaitable has resolved.

Answer-16: Nullable types are denoted by a ? before the type, allowing the value to be null, e.g., ?int.

Answer-17: Shapes are a flexible way to define data structures with specific fields and types, like lightweight objects.

Answer-18: Shapes are defined using the shape keyword, e.g., shape('name' => string, 'age' => int).

Answer-19: darray is a dictionary with key-value pairs, while varray is a vector-like array.

Answer-20: Enums are a way to define a fixed set of constant values, e.g., enum Color: string { RED = 'red'; }.

Answer-21: mixed represents any type of value and is used when the type is not known or varies.

Answer-22: Hack uses try-catch blocks for error handling, similar to PHP.

Answer-23: A tuple is an ordered, fixed-size collection of elements with specific types, e.g., (int, string).

Answer-24: Classes are defined using the class keyword, e.g., class MyClass {}.

Answer-25: This attribute ensures that subclasses use the same constructor signature as the parent class.

Answer-26: Generics allow defining classes and functions with type parameters for flexibility and reusability.

Answer-27: Vector is a mutable, ordered collection for storing values of the same type.

Answer-28: Map is an ordered collection of key-value pairs with unique keys.

Answer-29: The type keyword defines a type alias, e.g., type UserID = int;.

Answer-30: newtype defines a new type distinct from its base type, e.g., newtype Email = string;.

Answer-31: Interfaces are defined using the interface keyword and enforce method implementation in classes.

Answer-32: Traits are reusable pieces of code that can be included in classes to share functionality.

Answer-33: The __memoize attribute caches the results of a function for the same input parameters.

Answer-34: The is operator checks if a value is of a specified type, e.g., $x is int.

Answer-35: The as operator casts a value to a specified type or ensures a value is of that type.

Answer-36: Hack uses readonly properties and immutable collections to support immutability.

Answer-37: Hack lambdas are anonymous functions created using the => syntax.

Answer-38: AUTOLOAD is a magic method triggered when an undefined method or property is accessed.

Answer-39: A const is a class constant, which is a value that cannot be changed.

Answer-40: static methods belong to the class, while instance methods are tied to an object of the class.

Answer-41: Hack projects use a file structure compatible with PHP, often with an autoload.json for class loading.

Answer-42: Asynchronous collections like KeyedTraversable work with async functions for handling data streams.

Answer-43: dict is a type-safe dictionary for key-value pairs.

Answer-44: vec is a type-safe list for ordered collections.

Answer-45: Type constraints restrict the types a generic type parameter can accept.

Answer-46: Modules are a new feature that isolate code to prevent conflicts between libraries.

Answer-47: Hack uses Composer for dependency management, similar to PHP.

Answer-48: hh_autoload automatically loads classes and functions during runtime.

Answer-49: Yes, Hack supports Unicode through its string functions and libraries.

Answer-50: Hack runs on the HipHop Virtual Machine (HHVM).