Ruby Data Types

Ruby's core types cover the same ground as most languages, but as objects with a rich set of built-in methods rather than bare primitives.

Numbers

integer = 42
float = 3.14
big = 10_000_000        # underscores as visual separators, ignored by Ruby

puts 7 / 2      # 3   -- integer division truncates
puts 7.0 / 2    # 3.5 -- float division
puts 7.fdiv(2)  # 3.5 -- explicit float division without writing 7.0

Integer division silently truncating instead of raising an error is one of the most common early gotchas — if you need a precise result, make sure at least one operand is a float, or use fdiv.

Strings

single = 'no interpolation, no escapes except \\ and \''
double = "supports interpolation: #{1 + 1}, and escapes like \t and \n"

"ruby".length     # 4
"ruby".upcase     # RUBY
"  hi  ".strip    # "hi"
"a,b,c".split(",")  # ["a", "b", "c"]

Single-quoted and double-quoted strings aren't just a style choice: double quotes process #{} interpolation and escape sequences, single quotes mostly don't. Default to double quotes unless you specifically want the literal text.

Booleans and nil

is_ready = true
is_done = false
result = nil

nil represents "no value," similar to null elsewhere. The important quirk: in Ruby, only false and nil are falsy — everything else is truthy, including 0 and "", which are falsy in languages like JavaScript or Python.

puts "truthy!" if 0        # prints -- 0 is truthy in Ruby
puts "truthy!" if ""       # prints -- empty string is truthy too
puts "falsy!" unless nil   # prints -- nil is one of only two falsy values

This trips up almost everyone coming from another language, so it's worth internalizing early.

Arrays and hashes (a preview)

numbers = [1, 2, 3, "four", :five]   # arrays can mix types freely
user = { name: "Ada", age: 36 }       # a hash: key/value pairs

Both get a full lesson later in the Collections section — for now, just recognize the literal syntax: square brackets for an ordered list, curly braces for key/value pairs.

Checking and converting types

5.is_a?(Integer)     # true
5.is_a?(Numeric)      # true -- Integer and Float both descend from Numeric
5.class               # Integer

"42".to_i    # 42
42.to_s      # "42"
"3.14".to_f  # 3.14

Methods ending in ? conventionally return a boolean (is_a?, nil?, empty?) — that's a Ruby-wide naming convention, not special syntax, but it's followed consistently enough that you can rely on it when reading unfamiliar code.