array_re-evaulation.rb

# Normal has_many / belongs_to:
>> a = c.permitted_ips
=> []

# What we got back was just an Array:
>> a.class
=> Array

# Now build a new record:
>> c.permitted_ips.build :address => '123123'
=> #<PermittedIp id: nil, client_id: 14, description: nil, address: "123123", created_at: nil, updated_at: nil>

# All makes sense so far
# But now let's check `a` is still `[]`:
>> a
=> [#<PermittedIp id: nil, client_id: 14, description: nil, address: "123123", created_at: nil, updated_at: nil>]

# How has that happened? (`a` appears to have re-evaluated itself),