This issue is related to issue dart-lang/sdk#6496, but asks for less.

This comment was originally written by @seaneagan

Is this asking for:

• 2 separate optional parameters within the same declaration, one named, one positional
• allowing a single optional parameter to be both named and positional

The former could be solved by non-overlapping [] and {}. If overlapping [] and {} are allowed, then would have to decide whether to allow both {[ and [{ as well as }] and ]].

It is asking for non-overlapping [] and {}.
Examples:
new List([length = 0], {fill: null});
Stream.subscribe([onData], {onError, onDone})
new Date(year, [month, ...., milliseconds], {isUtc: false})

Added this to the Later milestone.
Added Accepted label.

This comment was originally written by @seaneagan

Sounds perfect! The only other thing I would change (also mentioned in issue dart-lang/sdk#6496) is to use = instead of : for named positional default values:

new List([length = 0], {fill = null});

The = to default positional optionals doesn't mimic call site syntax, so why does the named positional default syntax try to? I think it's more importatnt to be consistent between how to default optional parameters regardless of whether they are named or positional.

This comment was originally written by @rbishop-bah

Related: Issue dart-lang/sdk#17101

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

Removed Oldschool-Milestone-Later label.

Issue dart-lang/sdk#17101 has been merged into this issue.

Marked this as blocking dart-lang/sdk#21406.

Since 2.0 is thinking of some drastic changes is there any way the more extreme do like C#, Python, of dart-lang/sdk#6496 can be revisited.

@gbracha would a DEP be required for this?

@donny-dont if this issue is fixed then we will be able to do:

greet([String salutation = 'Hello'], {String who}) {
  print('$salutation $who!');
}

Then if there is really a need to allow parameters to be both named and positional, we could further allow something like this syntax:

greet({[String salutation = 'Hello', String who]}) {
  print('$salutation $who!');
}

But personally, I think that creates unnecessarily bloated API surface.

Any guesses when this might get implemented?