Question

What types in core scala library implement flatMap? I’ve seen it in Option and collections. Any other?

Answer 1

In short: all types which are monadic.

flatMap is such a common operation that there are a lot of types which can implement it. There are mainly two sort of types which implement it: containers and types which are useful to be sequenced. A small overview over some types:

The first category contains

• Collections like List, Seq, Set or Map (flatMap is defined is GenTraversableOnce)
• Container types like Option, Either (or better its Left- and RightProjection), Try (2.10), Future (2.10)

The second category contains

• Parsers (parser combinators)

A useful way to find out all method names called flatMap is to open Scaladoc on letter F (below the search bar). Then search for flatMap with your browser and you will find all types containing the method.