To make an object from a class, send the class the message `new`: `obj = Object.new`. `new` is a constructor method: it creates and returns a new instance of that class. A class can receive messages because Ruby classes are themselves objects. section 3.1
ticket = Ticket.new
puts ticket.event
`Ticket.new` creates a ticket instance; `ticket.event` then calls a method on that instance. The two calls have different receivers. section 3.1
Constructors can also accept arguments or a block that affects the resulting object. `Array.new` makes an empty array with no arguments. Give it a size and the positions start as `nil`; give it a second argument and every position starts with that value. section 9.2.1
Shared value or fresh value?
`Array.new(3, "abc")` puts the same string object in all three positions. Mutating that string through one position changes what you see through the others. Use `Array.new(3) { "abc" }` when each position needs a separate string: the block runs once per position. section 9.2.1
>> Array.new(3) { |i| 10 * (i + 1) } 1
=> [10, 20, 30] 2
The block receives each position’s index, so `Array.new(3) { |i| 10 * (i + 1) }` produces `[10, 20, 30]`. section 9.2.1
`new` is not the only way to obtain every kind of object: `[]` is a literal way to create an array. Conversely, some constructors produce objects that need cleanup. `File.new("code/ticket2.rb")` returns a file handle opened for reading if the file exists; otherwise it raises an exception. Close a handle opened this way when finished. section 9.2.1 section 12.2.1
