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Modules

Q: What is the function of modules in Ruby?

A: To provide namespaces. To provide a mechanism for multiple inheritance. To facilitate code reuse.

Q: What is the difference between a module and class?

A: A module cannot be instantiated.

Q: What is the difference between extend and include?

A: extend adds the instance methods of a module to a class as class methods. include adds the instance methods of a module to a class as instance methods.

Methods & blocks

Q: What are the three levels of method access control available in Ruby?

A: private: These methods are not accessible on instances of the class. They are only accessible internally when the receiver is self. protected: These methods are accessible internally to the class and within subclasses of the class. (TODO: expand answer) public: These methods are accessible everywhere, including on the instance.

Q: What are Procs in Ruby? How do they compare to closures in JS?

A: A Proc is essentially an anonymous function encapsulated as an object which can be passed around as a variable. Procs have access to the local variables from the context in which they were defined. Unlike in JS they do not have access to the self (analygous to this) of the context.

Exception handling

Q: How do you handle exceptions in Ruby code?

A: Using begin and rescue

Q: Why is it advised to rescue from StandardError rather than Exception?

A: StandardError is a subclass of Exception. Rescuing Exception rescues program signalling exceptions which are needed to signal, for example when a program should shut down.

Operators / Truthiness

Q: What is the difference between and/or and &&/||? What is the result of a = nil and true?

A: and and or have higher precedence than the assignment operator (=) whereas && and || have lower precedence. The result is that a is assigned the value nil and the result of the expression is nil.

Q: What values are "falsey" in Rails? Or, which values are "truthy"? What is the result of a = 0 || 1?

A: Only false and nil evaluate to false. Everything else is "truthy". The result is that a is assigned the value 0 and the result of the expression is 0.

Metaprogramming

**Q: What is the function of method_missing? How is it used in meta-programming in Ruby?

Poor performance.

**Q: What is a DSL (Domain Specific Language) and why is Ruby a popular language to build DSLs in?

TODO Other Questions

  • What are RubyGems? Got any favourites?
  • What is Rails good at? What is it not so good at?
  • List some things you would change about Rails
  • How does Rails extend the Ruby language? (Convenience methods, 3.seconds.ago, hash.slice, ...)
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