What does :: mean in Ruby?

Question

What does :: mean in Ruby? I see it used when calling a lot of gems.

Example:

ActiveRecord::Base.establish_connection(......

Answer 1

It accesses constants in a given class or module. E.g. ActiveRecord::Base is the constant Base defined in the module ActiveRecord.

Answer 2

It's called a scope resolution operator. Basically a fancy way of referencing a class within a namespace. ActiveRecord is the namespace and Base is the class.

Answer 3

According to ruby-doc.org:

When a receiver is explicitly specified in a method invocation, it may be separated from the method name using either a period “.” or two colons “::”. The only difference between these two forms occurs if the method name starts with an uppercase letter. In this case, Ruby will assume that a receiver::Thing method call is actually an attempt to access a constant called Thing in the receiver unless the method invocation has a parameter list between parentheses.

Answer 4

In the case you've shown, it is used to reference the module Base which is nested in module ActiveRecord. In effect, this defines a namespace hierarchy. See here for more details.