Understanding namespaces in Ruby

Question

In the code below:

::Trace.tracer = ::Trace::ZipkinTracer.new()

what is the relation between Trace and ZipkinTracer

Answer 1

ZipkinTracer is inside of Trace namespace, like this:

module Trace
  class ZipkinTracer
  # ...
  end
end

The :: before constant name means that you point to the root. For example in the following code:

class Class1
end

module Module1
  class Class1
  end

  def foo
    ::Class1
  end
end

::Class1 ensures that you refer to the "root" Class1. If you had:

def foo
  Class1
end

the Module1::Class1 would be referred.