Don't Panic: Ruby Fundamentals

Ruby is a programming language where the running values are objects and most work is a method call sent to one of them. That sounds like an invitation to anthropomorphize a String. Resist the urge. The useful part is that a program can be understood as values receiving behavior, returning new values, and occasionally doing something noticeable, such as writing a file.

The first useful mental anchor is assignment. A variable is a name that refers to an object. Giving the same Array two names does not create an Array twin in a tiny hat. It creates two ways to reach the same object. Mutation changes that shared object, while an ordinary assignment only changes which object a name refers to. This explains a surprising number of later bugs without requiring a séance with the debugger.

The second anchor is the block, which is behavior handed to a method. A collection method can use that behavior to visit, transform, filter, or combine its values. Keep the block small enough that its purpose stays visible. When it starts carrying policy, branches, and failure handling, give that work a named method. Ruby is concise, but a compressed decision is still a decision that somebody must read.

Then comes the method boundary. Parameters, return values, mutation, and errors all need to be visible there. Ruby returns its last expression by default, and only nil and false are falsey. An empty Array and zero are not secret requests to take the other branch. Check the condition that you actually mean.

Ruby also has gems, packaged code managed in a project through a Gemfile and Bundler. The lockfile records the selected dependency graph, so changing it changes the program's operating conditions. Treat that change as code, test the result, and keep the language boundary separate from a framework's habits.

For the detailed map, read the Intro when an object, method, module, or exception needs its full explanation. Use the Slides when the relationships need to fit on one page. Keep the Cheatsheet nearby while writing code. The practice reference and exercise turn these ideas into commands and observable results. The quiz is where the innocent-looking details wait with a clipboard.