class OpenTelemetry::Context::Propagation::TextMapGetter

key from a carrier that implements [] and a keys method
The default getter module provides a common methods for reading

def get(carrier, key)

operations.
Reads a key from a carrier that implements +[]+. Useful for extract 
def get(carrier, key)
  carrier[key]
end

def keys(carrier)

keys.
Reads all keys from a carrier. Useful for iterating over a carrier's 
def keys(carrier)
  carrier.keys
end