Function class_of 

pub fn class_of(arguments: &[OsString]) -> ChildClass

What: The class of the Git step a request runs. Why: A step is a query only when its subcommand is named in PLUMBING_SUBCOMMANDS; every other step, a request with no subcommand included, gets the longer bound.

In TS you’d write (pseudocode):

QUERIES.includes(subcommandOf(args)) ? 'plumbing' : 'object'