code: func NewPortAllocator(pr net.PortRange) *PortAllocator {
  	return NewPortAllocatorCustom(pr, func(max int, rangeSpec string) allocator.Interface {
  		return allocator.NewAllocationMap(max, rangeSpec)
  	})
  }
docs: // Helper that wraps NewPortAllocatorCustom, for creating a range backed by an in-memory store.