code: func GetOrRegisterHistogram(name string, r Registry, s Sample) Histogram {
  	if nil == r {
  		r = DefaultRegistry
  	}
  	return r.GetOrRegister(name, func() Histogram { return NewHistogram(s) }).(Histogram)
  }
docs: // GetOrRegisterHistogram returns an existing Histogram or constructs and
  // registers a new StandardHistogram.