I’m told that this chapter is best accompanied by a rag. Something you can mop your face with as the sweat pours off. We’ll be covering a lot of Ruby in a short time. Names and types and variables and objects. Methods and classes and modules. It’s not hard. It’s actually quite lovely. But there is a lot of it.
“My conscience won’t let me call Ruby a computer language. That would imply that the language works primarily on the computer’s terms. That the language is designed to accommodate the computer, first and foremost. That therefore, we, the coders, are foreigners, seeking citizenship in the computer’s locale.”
Numbers
5 # integer 3.14 # float 2_000_000 # underscores for readability — still just a number 0xFF # hexadecimal: 255 0b1111 # binary: 15
Strings
"chunky bacon" # double-quoted
'also a string' # single-quoted (no interpolation)
"chunky #{4 - 2}" # => "chunky 2"
"line one
line two" #
is a newline
%Q(this works too) # another way to make a string
Symbols
:chunky :bacon :a_longer_symbol
A symbol is like a string that doesn’t change. It always refers to the same object in memory. Symbols are used as keys in hashes, as method names, as identifiers. They start with a colon.
Arrays
animals = ['fox', 'dog', 'cat']
animals[0] # => 'fox'
animals[-1] # => 'cat' (negative: count from end)
animals[1..2] # => ['dog', 'cat'] (a range)
animals.first # => 'fox'
animals.last # => 'cat'
animals.length # => 3
animals.include?('fox') # => true
animals.push('wolf') # add to end
animals.unshift('bear') # add to beginning
animals.map { |a| a.upcase } # => ['BEAR', 'FOX', 'DOG', 'CAT', 'WOLF']
animals.select { |a| a.length > 3 } # => ['wolf']
Hashes
blix = { name: 'Trady Blix', age: 9, color: :black }
blix[:name] # => 'Trady Blix'
blix[:age] # => 9
blix.keys # => [:name, :age, :color]
blix.values # => ['Trady Blix', 9, :black]
blix[:weight] # => nil (missing keys return nil, not an error)
Hashes are the workhorses of Ruby. You will use them constantly. Any time you want to store key-value pairs — configuration, attributes, options — use a hash.
True, False, Nil
!!nil # => false (nil is falsy) !!false # => false (false is falsy) !!0 # => true (0 is truthy in Ruby — unlike some languages!) !!"" # => true (empty string is truthy!) !!"any string" # => true
In Ruby, only nil and false are falsy. Everything else — including 0 and empty string — is truthy. This surprises people coming from Python or JavaScript.
Methods
def double(x) x * 2 end double(5) # => 10 double 5 # also fine — parentheses optional in many cases
In Ruby, the last expression evaluated in a method is automatically the return value. You don’t need an explicit return, though you can use one if you want to return early.
Blocks
3.times { puts "hello" }
[1, 2, 3].each do |n|
puts n * 10
end
# => 10
# => 20
# => 30
Blocks are the soul of Ruby. They are chunks of code you can pass to methods. The curly braces or do...end wrap the block. The |n| is the block parameter — the thing the method passes in to the block each time it calls it.
