Need many objects with the same behavior? Define a class rather than adding methods to each object separately. `Ticket.new` sends `new` to the class object `Ticket` and returns a new instance. Methods defined in `Ticket` can then serve every ticket, while each ticket remains a distinct object. section 3.0 section 3.1
A class creates instances
`class Ticket; def event; "Concert"; end; end` defines an instance method. After `ticket = Ticket.new`, `ticket.event` returns `"Concert"`. The receiver of `new` is the class; the receiver of `event` is the ticket. section 3.1
`Ticket` is itself an object: an instance of Ruby’s built-in class `Class`. A class can receive messages, be passed as a method argument, and have methods added to it. `Class.new` creates a class object, just as `Ticket.new` creates a ticket. The new class need not immediately have a constant name: `my_class = Class.new` followed by `my_class.new` creates an instance through a local variable. section 3.6 section 3.6.1
c = Class.new do
def say_hello
puts "Hello!"
end
end
The `Class.new` block defines an instance method while creating an anonymous class; instances made with `c.new` can call `say_hello`. section 3.6.1
Class objects get methods much as other objects do. `Ticket.new` works because `new` is an instance method of `Class`. `Class` inherits from `Module`, so a class object can also use methods such as `attr_reader` and `attr_accessor`. Inside a class definition, the class object is `self`: bare calls to those attribute methods go to that object. section 3.6.2 section 5.1.1
A method on the class object is not automatically a method on its instances. If `Ticket.most_expensive` exists, calling `most_expensive` on an individual ticket fails unless that ticket has an applicable method of its own. This distinction separates class-level utility behavior from instance behavior. section 3.6.5
Classes can be reopened: two `class C` blocks that define different methods add both methods to `C`. This can support deliberate extensions across files, but scattered definitions can be harder to follow. Classes can also be nested in modules and named through constants such as `Tools::Hammer`; that notation alone does not reveal whether a named constant holds a class or another kind of value. section 3.1.3 section 4.4.2
