Gain insights into Ruby development with 78 tasks tailored for beginners and experienced coders. Explore object-oriented concepts, debug programs, and advance your freelance coding career.

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This self-study course written as a book is your first step towards making money by coding and programming from home, and having fun doing it. You will understand how the Ruby language works, and establish a foundation for being a successful freelance developer. This course gives you not only technical detail, but presents knowledge in a friendly format, understandable by all ages, providing a thorough explanation of modern concepts for absolute beginners.

In this course you will find 78 easy to follow tasks, so even people without any programming skill can solve them. Beginners will learn how to create, debug, and understand programs in Ruby. Those who are already familiar with the language will rediscover object-oriented concepts, memory organization, find career advice, and save the planet from a nuclear apocalypse.

Ready to dive into one of the most influential and demanding third generation programming languages? Let's tune in!

The Handbook for Ruby Developers

# Listing all keys in a hash
There is a way in Ruby language to list all the keys in a hash. Here is how this method works:

```ruby
$ pry
> hh = {}
=> {}
> hh[:red] = 'ff0000'
=> "ff0000"
> hh[:green] = '00ff00'
=> "00ff00"
> hh[:blue] = '0000ff'
=> "0000ff"
> hh.keys
=> [:red, :green, :blue]
```

We defined a hash and pushed a few key-value pairs in it. Keys are a type of symbol, and values are just strings. These strings (`ff0000`, `00ff00`, and `0000ff`) are conventional three-byte representations of the color code `RGB`, where the first byte is responsible for red (`R`) color, the second for green (`G`), and the third for the blue (`B`).
 
Getting the list of hash keys isn’t often required. However, there is a need to use keys only in a hash.


# Sets
A programmer is free to use hash data structure and arbitrary data for values—like `true`, for example—but a special hash-like data structure is designed to keep keys only, without any values. The common name of this data structure is hash set. In Ruby, it’s represented by the `Set` class):

> **Note:** `Set` implements a collection of unordered values with no duplicates.

In other words, a **set** is a collection of items that usually originate from a common source.

Let’s practice understanding a hash set a little bit more. Given an English sentence, find out if all the letters of the alphabet were used in this particular sentence. For example, the sentence “Quick brown fox jumps over the lazy dog” is commonly used to test typewriters, printers, fonts, and so on because it uses all the letters of the English alphabet. If we omit the first word, “quick”), we won’t find the letter “q” in the phrase “brown fox jumps over the lazy dog.”


# Method example
We’ll create a method that will return `true` if all the letters of the English alphabet were used for the provided string, otherwise it will return `false`. How should we approach this problem? It’s actually pretty straightforward. We’ll iterate over each character in a given string, and if it’s not a space, we’ll add it to the hash, regardless of its existence in the hash, since keys in a hash are always unique and aren’t duplicated. Since there are no duplicates in a hash, we can only have 26 records maximum, one record for each letter of the English alphabet.

But there is something that feels off in this challenge. If we use a classic hash, we need to set keys and values. Value, in this case, will be useless:

```ruby
hh[letter] = true
```

`true`, `false`, `1`, `0` or any string is fine as the value in the line above because we do not check it later. We rely on the hash data structure and check the `size` property, but we never use the value. In other words, we’re wasting computer memory for the values we don’t need. 

This is where a hash set data structure comes into play. Here is how our program listing looks when we use a hash set, represented by the `Set` class:


Learn what hash sets are and how to use them in Ruby.

Before We Begin

First Steps

Fundamentals of Ruby

Conditional Statements

Operators and Methods

Arrays

Hash

Fun with Object Oriented Programming

Debugging in Ruby

Ruby Version Manager

Testing Ruby Programs

Wrap Up!

Appendix

HashSets

Listing all keys in a hash