E0032

Warning name: unused_default_value

Default value of optional argument is unused. This implies at every call site of this function, the optional argument is always explicitly supplied with a value. This means the optional argument can be refactored into a labelled argument.

Erroneous example

Note, this warning is turned off by default. To enable this warning, you need to modify the "warn-list" of moon.pkg.json:

moon.pkg.json

{
  "is_main": true,
  "warn-list": "+unused_default_value"
}

main.mbt

///|
fn f(opt~ : Int = 4) -> Int {
  ignore(opt)
  0
}

///|
fn main {
  println(f(opt=3))
  println(f(opt=3))
}

Suggestion

Turn the optional argument into a labelled argument:

///|
fn f(opt~ : Int) -> Int {
  ignore(opt)
  0
}

///|
fn main {
  println(f(opt=3))
  println(f(opt=3))
}