scala - Why foreach fail with String typed List with toUpperCase? -

from programming in scala,we know foreach high-order function takes procedure return type unit.so think following slice work:

val abcde = list("a","b","c","d","e") abcde.foreach(print _.touppercase)

however tells me that:

1: error: ')' expected '.' found.   abcde foreach (println _.touppercase)                           ^

but these 2 below both work well:

println("abcde".touppercase) abcde.foreach(print _)

so what's difference?

these 2 using _ in different ways:

abcde.foreach(print _.touppercase) abcde.foreach(print _)

in first case, have anonymous function _ denotes placeholder parameter.

in second case, _ means you'd function value method print (an eta expansion).

so comparing 2 irrelevant.

more point this:

scala> print "abcde".touppercase <console>:1: error: ';' expected string literal found.        print "abcde".touppercase              ^

as can see, doesn't work, replacing "abcde" _ wouldn't work either.

Funaction