Variables & Data Types

📦 Variables & Data Types

✏️ Variables — No Declaration Keyword

Ruby variables need no declaration keyword and no sigil — just assign a name and Ruby infers the type from the value, exactly like Python. This is a step further than PHP, which requires the $ sigil on every variable reference, not just at declaration:

Copyage = 33              # no $ sigil, no let/var/val keyword
name = "Philip"
is_ready = true     # snake_case is Ruby's naming convention, like Python

Ruby variable names use snake_case by convention (like Python; PHP's convention varies between snake_case and camelCase depending on the codebase). Variable names are entirely lowercase by convention too — a name starting with a capital letter means something different in Ruby, as you'll see once classes and constants show up in later chapters.

🔤 Strings — Single vs Double Quotes Actually Matter

Both single and double quotes create strings, but unlike PHP (where the same distinction exists) they aren't interchangeable — only double quotes support interpolation and escape sequences:

Copyname = "Philip"

puts "Hello, #{name}!"   # Hello, Philip!  -- double quotes interpolate
puts 'Hello, #{name}!'   # Hello, #{name}! -- single quotes are literal

puts "Line one\nLine two" # \n becomes a real newline in double quotes
puts 'Line one\nLine two' # \n stays as literal backslash-n in single quotes

Common string methods: "ruby".upcase → "RUBY", "RUBY".downcase → "ruby", "ruby".length → 4, "ruby".reverse → "ybur", and concatenation with + or repetition with * ("ab" * 3 → "ababab").

🔢 Numbers — Watch Out for Integer Division

Copy10 / 3       # => 3   -- Integer / Integer stays an Integer, truncated
10.0 / 3     # => 3.3333333333333335  -- a Float on either side forces Float division
10.fdiv(3)  # => 3.3333333333333335  -- explicit float division method

🔖 Symbols — The New Concept

A symbol is a lightweight, immutable identifier written with a leading colon: :name, :status, :pending. Neither PHP nor Python has a direct equivalent — the closest PHP gets is a bare string constant, and the closest Python gets is an enum member, but neither carries Ruby's specific guarantee: every instance of the same symbol in a running program is the exact same object in memory.

Copy:pending.object_id == :pending.object_id   # => true  -- always the same object
"pending".object_id == "pending".object_id # => false -- two different String objects

📚 Arrays

Copyfruits = ["apple", "banana", "cherry"]

fruits[0]        # => "apple"   -- zero-indexed, same as PHP/Python
fruits[-1]       # => "cherry"  -- negative indexing, same as Python (PHP has no native equivalent)
fruits.length     # => 3
fruits << "date"    # append -- equivalent to fruits.push("date")
fruits.first      # => "apple"
fruits.last       # => "date"

Ruby arrays are ordered, can hold mixed types in the same array (like PHP and Python lists), and the << "shovel" operator for appending is Ruby-specific — PHP uses $arr[] = $value, Python uses .append(value).

🗝️ Hashes

A hash is Ruby's key-value structure — directly comparable to a PHP associative array or a Python dict. Modern Ruby code almost always uses symbol keys with a shorthand syntax:

Copy# Modern shorthand (symbol keys) -- the style you'll see most often
person = { name: "Philip", age: 33 }
person[:name]     # => "Philip"

# Old "hashrocket" syntax -- still required for non-symbol keys, like strings
scores = { "Philip" => 95, "Alex" => 88 }
scores["Philip"]  # => 95

🕳️ nil — Ruby's "Nothing"

nil is Ruby's equivalent of PHP's null or Python's None — it represents the absence of a value. The important, easy-to-miss detail: in a boolean context, Ruby treats only two values as falsy — nil and false. Everything else, including 0 and "" (empty string), is truthy.

Copyif 0
  puts "0 is truthy in Ruby!"   # this DOES print
end

value = nil
value.nil?           # => true -- the idiomatic way to check for nil

💻 Coding Challenges

🎯 What's Next

Next chapter: Control Flow — if/unless, case/when, loops (while, until, for, each), and what it means for Ruby to be expression-oriented — where even an if statement returns a value you can assign.