The other concept that GP needs to understand the title is https://en.wikipedia.org/wiki/Futures_and_promises https://en.wikipedia.org/wiki/Futures_and_promises

The other concept that GP needs to understand the title is https://en.wikipedia.org/wiki/Futures_and_promises https://en.wikipedia.org/wiki/Futures_and_promises So the title/TFA is about "futures" (in the sense of my link) that have "zero cost" (in the sense of steveklabnik's comment).