Ruby interviews go two layers deep: the language itself — blocks, modules, the method lookup chain — and then Rails, where most questions are really about ActiveRecord and the database underneath it. Below are the questions asked most often, each with a model answer. Junior: core theory, definitions, and simple practical cases.
Only nil and false are falsy — 0, '' and [] are all truthy. This trips up anyone arriving from JavaScript or Python. It means if list is true even for an empty list, so when you mean empty you have to say list.empty?.
nil? asks whether the object is nil. empty? asks whether a string, array or hash has no elements — and it explodes on nil, because nil has no empty?. blank? comes from Rails and covers both plus whitespace-only strings, which is why it is the one you usually want on form input.
A symbol is immutable and reused — :name is the same object everywhere. A string literal creates a new object each time. Use symbols for names of things (hash keys, statuses) and strings for text you show or change.
It defines a getter and a setter for an instance variable, so you do not write them by hand. attr_reader gives only the getter, attr_writer only the setter. Reaching for attr_accessor by default is a habit worth breaking — most attributes should not be writable from outside.
A chunk of code handed to a method with do...end or { }. Inside the method yield runs it, and block_given? tells you whether one arrived. each and map are ordinary methods — there is no special syntax making them work, just blocks.
The model holds data and the rules about it, the controller receives the request and decides what to do, the view renders the response. The practical rule: business logic belongs in the model or a service object, not the controller, and a view that queries the database is a view doing the controller's job.
A migration is a versioned change to the database — a Ruby file you run forward. schema.rb is the generated snapshot of the current structure, which is what a new machine loads instead of replaying every migration since the beginning. You edit migrations; you do not hand-edit the schema file.
In a real interview you speak under pressure. Cam asks these same questions, scores every answer, and shows exactly what to fix.
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