syntax - Is there a difference between :: and . when calling class methods in Ruby?

Question

Simple question, but one that I've been curious about...is there a functional difference between the following two commands?

String::class
String.class

They both do what I expect -- that is to say they return Class -- but what is the difference between using the :: and the .?

I notice that on those classes that have constants defined, IRB's auto-completion will return the constants as available options when you press tab after :: but not after ., but I don't know what the reason for this is...

Answer 1

The . operator basically says "send this message to the object". In your example it is calling that particular member. The :: operator "drills down" to the scope defined to the left of the operator, and then calls the member defined on the right side of operator.

When you use :: you have to be referencing members that are defined. When using . you are simply sending a message to the object. Because that message could be anything, auto-completion does not work for . while it does for ::.