Why not StringBuilder= (string) in scala?

This behavior seems to be broken (I'm using scala 2.9.1)

var b= new StringBuilder

All right:

b+='a'
b.append('b') 
b.append("de")

This results in compilation errors:

b+="de"

Any idea, why only StringBuilder #= (C: char) exists, and StringBuilder #append (C: char) and StringBuilder #append (s: String) coexist happily? What is the problem with declaring and implementing StringBuilder #= (s: String)?

Are there any monitoring or deeper problems in the scala type system?

Solution

Try B = "de" Strings are considered a collection of chars