Objects

Everything is Ruby is an object, the Object class is the parent class of all classes in Ruby. Its methods are therefore available to all objects unless explicitly overridden.

An important method in the Object class is class(). It returns the “type” of an object.

> 1.class()              # => Fixnum
> 1.class                # => Fixnum
> 1.0.class              # => Float
> "Foo".class  # => String

Notice how parentheses are optional – they are commonly omitted.

The language syntax is sensitive to the capitalization of identifiers, in most cases treating capitalized variables as constants.

Variables

Ruby does not use variable declarations, if you assign a value to a literal, an “appropriate” variable named after that literal is created.
Example

> a = 2    # => 2
> a        # => 2

In this example, a has type Fixnum, this is an integer data in Ruby. The other integer type is Bignum (represents numbers of arbitrary size).
Example

> a = "2"       # => "2"
> a             # => "2"

Now a is a String variable.

Important: All assignments are done by reference in Ruby. I.e, a variable just holds a reference to an object, and does not care about the type of the object.

Ruby supports parallel assignment.
Example: You can easily swap the values stored in two variables:

> a = 2         # => 2
> b = 1         # => 1
> puts a, b     # 2
                # 1
                # => nil
a, b = b, a     # => [1, 2]

Ruby uses simple naming conventions to denote the scope of variables:

• name – could be a local variable.
• @name – an instance variable.
• @@name – a class variable.
• $name – a global variable.

The @ and $ sigils enhance readability by allowing the programmer to easily identify the roles of each variable.

Furthermore, local variables must begin with a lowercase letter, and the convention is to use underscores, rather than camel case, for multi-word names.

Constants are any name that starts with an uppercase letter, and the convention is to use underscores.

Classes and modules are treated as constants, so they begin with uppercase letters, and the convention is to use camel case.