Why does the Scala compiler disallow overloaded methods with default arguments?

Question

While there might be valid cases where such method overloadings could become ambiguous, why does the compiler disallow code which is neither ambiguous at compile time nor at

Answer 1

I'd like to cite Lukas Rytz (from here):

The reason is that we wanted a deterministic naming-scheme for the generated methods which return default arguments. If you write

def f(a: Int = 1)

the compiler generates

def f$default$1 = 1

If you have two overloads with defaults on the same parameter position, we would need a different naming scheme. But we want to keep the generated byte-code stable over multiple compiler runs.

A solution for future Scala version could be to incorporate type names of the non-default arguments (those at the beginning of a method, which disambiguate overloaded versions) into the naming schema, e.g. in this case:

def foo(a: String)(b: Int = 42) = a + b
def foo(a: Int)   (b: Int = 42) = a + b

it would be something like:

def foo$String$default$2 = 42
def foo$Int$default$2 = 42

Someone willing to write a SIP proposal?