class Datadog::Tracing::Correlation::Identifier

@public_api
Represents current trace state with key identifiers

def initialize(

@!visibility private 
def initialize(
  env: nil,
  service: nil,
  span_id: nil,
  span_name: nil,
  span_resource: nil,
  span_service: nil,
  span_type: nil,
  trace_id: nil,
  trace_name: nil,
  trace_resource: nil,
  trace_service: nil,
  version: nil
)
  # Dup and freeze strings so they aren't modified by reference.
  @env = Core::Utils::SafeDup.frozen_dup(env || Datadog.configuration.env)
  @service = Core::Utils::SafeDup.frozen_dup(service || Datadog.configuration.service)
  @span_id = span_id || 0
  @span_name = Core::Utils::SafeDup.frozen_dup(span_name)
  @span_resource = Core::Utils::SafeDup.frozen_dup(span_resource)
  @span_service = Core::Utils::SafeDup.frozen_dup(span_service)
  @span_type = Core::Utils::SafeDup.frozen_dup(span_type)
  @trace_id = trace_id || 0
  @trace_name = Core::Utils::SafeDup.frozen_dup(trace_name)
  @trace_resource = Core::Utils::SafeDup.frozen_dup(trace_resource)
  @trace_service = Core::Utils::SafeDup.frozen_dup(trace_service)
  @version = Core::Utils::SafeDup.frozen_dup(version || Datadog.configuration.version)
end

def to_h 

def to_h
  @to_h ||= {
    # Adds IDs as tags to log output
    dd: {
      # To preserve precision during JSON serialization, use strings for large numbers
      env: env.to_s,
      service: service.to_s,
      version: version.to_s,
      trace_id: trace_id.to_s,
      span_id: span_id.to_s
    },
    ddsource: Core::Logging::Ext::DD_SOURCE
  }
end

def to_log_format

but the algorithm makes the constants implicit. Hence, we use it for validation during test.
This method (#to_log_format) implements an algorithm by prefixing keys for nested values 
def to_log_format
  @log_format ||= begin
    attributes = []
    attributes << "#{LOG_ATTR_ENV}=#{env}" unless env.nil?
    attributes << "#{LOG_ATTR_SERVICE}=#{service}"
    attributes << "#{LOG_ATTR_VERSION}=#{version}" unless version.nil?
    attributes << "#{LOG_ATTR_TRACE_ID}=#{trace_id}"
    attributes << "#{LOG_ATTR_SPAN_ID}=#{span_id}"
    attributes << "#{LOG_ATTR_SOURCE}=#{Core::Logging::Ext::DD_SOURCE}"
    attributes.join(' ')
  end
end

def trace_id

DEV-2.0: This public method was returning an Integer, but with 128 bit trace id it would return a String. 
def trace_id
  if Datadog.configuration.tracing.trace_id_128_bit_logging_enabled &&
      !Tracing::Utils::TraceId.to_high_order(@trace_id).zero?
    Kernel.format('%032x', @trace_id)
  else
    Tracing::Utils::TraceId.to_low_order(@trace_id)
  end
end