Swift version: 5.1
A functor is any data type that can be mapped over using
map(), as long it abides by two laws:
map(), the result should be the same as mapping first A then B individually.
Both of those laws sound obvious, but that doesn’t mean they aren’t important. Arrays are functors, sets are functors, optionals are functors, and more.
SAVE 20% ON iOS CONF SG The largest iOS conference in Southeast Asia is back in Singapore for the 5th time in January 2020, now with two days of workshops plus two days of talks on SwiftUI, Combine, GraphQL, and more! Save a massive 20% on your tickets by clicking on this link.
Available from iOS 8.0 – learn more in my book Pro Swift
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.