Scala language proposals for defaults, .copy and overrides

defaults-and-copy-ideas.scala

// DEFAULT VALUES

def foo(str: String = "test") = ???
assert( foo.str == "test" ) // new: named access to default values

case class Bar(str: String = "test")
assert( Bar.apply.str == "test" ) // same for case classes via .apply method

// REPETIION-FREE .copy (aka lenses light)

case class Baz(bar: Bar)
val b = Baz( Bar( "world" ) )
assert(
  b.copy( bar = b.bar.copy( str = "hello, " ++ b.bar.str ) ) // old: having to repeat repeat b and b.bar
  == b.copy( bar _= _.copy( str _= "hello, " ++ _ ) ) // new: short version via ~= operator for modification (alt syntax ~=)
)
// new short version desugars to this (using access to default values):
b.copy( bar = b.copy.bar.copy( str = "hello, " ++ b.copy.bar.copy.str ) )

// MODIFYING OVERRIDES

class Foo{ def str = "world" }
assert(
  new Foo{ override str = "hello, " ++ super.str }.str // having to repeat `str` in override
  == new Foo{ override str _= "hello, " ++ _ }.str // new: modifying function based on parent value (alt syntax ~=)
)