Description

Currently, calling array.join on an empty array returns none. There should be a default argument, similar to the one on array.sum or array.product, defining the value to return for an empty array (defaulting to none).

Use Case

It is easier to write arr.join(", ", default: "") than

#if arr.len() == 0 {
  ""
} else {
  arr.join(", ")
}

Drawbacks

As mentioned in #6780 (comment), the proliferation of default arguments may indicate than a more general solution should be implemented. In the meantime, this proposal makes sense.