Ruby Interview Questions and Answers

Answer: Container for methods and constants; used for mixins

Modules group methods/constants. Use for namespacing and mixins. module MyModule; end. Include for instance methods, extend for class methods. Cannot instantiate.

Answer: Hidden class unique to each object

Singleton class is hidden class for each object. Access with class << obj. Define singleton methods here. Understanding crucial for metaprogramming. Part of Ruby object model.

Answer: Dynamic, object-oriented programming language

Ruby is a dynamic, interpreted, object-oriented programming language created by Yukihiro Matsumoto (Matz). Focuses on simplicity and productivity with elegant syntax.

Answer: Principle of Least Surprise (POLA)

Ruby follows POLA (Principle of Least Surprise) - the language should behave in a way that minimizes confusion. Designed to be intuitive and natural.

Answer: include adds instance methods, extend adds class methods

include mixes module methods as instance methods. extend mixes as class methods. prepend inserts before (override). Use for different composition needs.

Answer: Opens singleton class for defining class methods

class << self opens singleton class. Define class methods here. Alternative to self.method. More common in gems/frameworks. Cleaner for multiple class methods.

Answer: Called when constant not found

const_missing called when constant undefined. Implement autoloading, lazy loading. Rails uses for autoloading. Powerful but can hide errors. Define on module/class.

Answer: Anonymous function with -> or lambda

Lambda: square = ->(x) { x * 2 } or lambda { |x| x * 2 }. Call with .call(). Strict argument checking. return exits lambda only. Closure captures variables.

Answer: puts or print

Use puts (adds newline) or print (no newline). p for debugging (shows inspect output). puts most common for output. Example: puts "Hello World".

Answer: Order Ruby searches for methods

Method lookup: object → singleton class → class → included modules (reverse order) → superclass → ... → BasicObject. Use .ancestors to see chain. Important for understanding behavior.

Answer: name = value (no declaration keyword)

Variables declared by assignment: name = "John". No var/let keyword. Lowercase/underscore for local variables. Dynamic typing - type determined at runtime.

Answer: Object that holds block of code

Proc is object wrapping block: proc = Proc.new { |x| x * 2 }. Call with .call(). Lenient arguments. return exits enclosing method. Convert block to object.

Answer: local_var, @instance_var, @@class_var, $global, CONSTANT

local_variable (snake_case), @instance_variable, @@class_variable, $global_variable, CONSTANT (uppercase). Conventions indicate scope. Very important in Ruby.

Answer: Includes module before class in lookup chain

prepend inserts module before class in lookup. Methods override class methods. Use for wrapper/decorator pattern. Ruby 2.0+ feature. More powerful than include.

Answer: Lambda strict args and return; Proc lenient

Lambda: strict argument checking, return exits lambda. Proc: lenient arguments, return exits enclosing method. Lambda more like method. Choose based on needs.

Answer: Immutable identifier starting with :

Symbol is immutable identifier: :name, :status. More memory efficient than strings. Same symbol has same object_id. Use for hash keys, identifiers.

Answer: Calls block passed to method

yield executes block passed to method. def greet; yield "Hello"; end. Call: greet { |msg| puts msg }. block_given? checks if block passed. Implicit block passing.

Answer: Scoped monkey patching

Refinements scope monkey patches: refine String { def shout; upcase; end }. Use with using. Lexically scoped modifications. Safer than global monkey patching.

Answer: Lightweight concurrency primitive

Fiber provides cooperative concurrency. Create with Fiber.new. Control with resume/yield. More lightweight than threads. Use for generators, async programming.

Answer: Symbols immutable, unique; strings mutable, multiple instances

Symbols are immutable, one instance per value. Strings are mutable, new instance each time. Use symbols for identifiers, strings for text data.

Answer: Checks if block passed to method

block_given? returns true if block passed. Use to make blocks optional: yield if block_given?. Avoids errors when no block. Good defensive programming.

Answer: True concurrency with OS threads

Thread provides real OS threads. Thread.new { code }. Use Mutex for synchronization. GIL limits parallelism in MRI. Better for I/O than CPU-bound. Thread-safe coding needed.

Answer: def method_name; end

Define methods with def: def greet(name); "Hello #{name}"; end. Implicit return (last expression returned). Convention: snake_case names, ? for predicates, ! for mutating.

Answer: Converts block to Proc or Proc to block

& converts: block to Proc in parameters (def method(&block)), Proc to block in calls (method(&proc)). Explicit block handling. Enables passing blocks as objects.