Need help to understand how scala list.contains works -

this question has answer here:

• scala: why seq.contains take argument, instead of argument of sequence type? 3 answers

why like:

val map = map(....)  list(1,2,3,4).contains(map) 

or

list(1,2,3,4).contains("hello") 

are allowed compile. though scala type safe.

if consult scaladocs list.contains, notice following method signature:

def contains[a1 >: a](elem: a1): boolean

of particular interest type parameters, [a1 >: a] if break down, get:

• a, type of elements list contains
• a1, type of element searching in list
• >:, symbol representing lower bound

this should interpreted a1 lower bounded a, a1 either of type or more generic type. see http://www.scala-lang.org/old/node/137 more information lower type bounds.

you have list of int. ask if list contains string. since any >: string , any >: int, compiler doesn't complain. same circumstances apply map scenario.