class Grape::Validations::ParamScopeTracker

Use .current to access the instance for the running request.
Lifecycle is managed by Endpoint#run_validators via .track.
objects can serve as keys without relying on value equality.
instances. Both trackers are identity-keyed hashes so that ParamsScope
Holds per-request mutable state that must not live on shared ParamsScope

def self.current 

def self.current
  Fiber[FIBER_KEY]
end

def self.track 

def self.track
  previous = Fiber[FIBER_KEY]
  Fiber[FIBER_KEY] = new
  yield
ensure
  Fiber[FIBER_KEY] = previous
end

def index_for(scope) 

def index_for(scope)
  index_tracker[scope]
end

def index_tracker 

def index_tracker
  @index_tracker ||= {}.compare_by_identity
end

def qualifying_params(scope)

by callers (both yield a blank result that falls through to the parent params).
Note: an explicitly stored empty array and "never stored" are treated identically
Returns qualifying params for +scope+, or EMPTY_PARAMS if none were stored. 
def qualifying_params(scope)
  qualifying_params_tracker.fetch(scope, EMPTY_PARAMS)
end

def qualifying_params_tracker 

def qualifying_params_tracker
  @qualifying_params_tracker ||= {}.compare_by_identity
end

def store_index(scope, index) 

def store_index(scope, index)
  index_tracker.store(scope, index)
end

def store_qualifying_params(scope, params) 

def store_qualifying_params(scope, params)
  qualifying_params_tracker.store(scope, params)
end