Learning Functional Programming in Go

Methods can query other objects' methods internally for data required to make decisions

So, instead of calling the GetTravelTime(startLocation, endLocation) method, it would be better to call GetTravelTime()?

Where would we get the startLocation and endLocation values from?

How can we be sure that there aren't other values, such as modeOfTransportation, that would impact our travel time result?

Doesn't that create internal, undocumented dependencies (assuming we document our external APIs)?