Swift performance and CustomStringConvertible protocol

Question

Here I'm trying to benchmark my distinct function, which receive array of random objects and return distinct array, by removing duplicates by phoneNumber attribute: The strange thing happens when I implement CustomStringConvertible protocol for my Person class - the time spent for the task increases 3 times (see the elapsed time in very last line)

I never print any Person object so I don't see obvious reason for description var being accessed for 21000 times. Here is the result when I'm not implementing the CustomStringConvertible protocol:

What is the reason for the performance drop?

Answer 1

I bet the playground is using the description property to display it in the results on the right side timeline view. Try running this outside of a playground and see what happens.