DartPad keeps saying expecting 2, receiving 3 arguments in constructor - dart

Question

Email( List<String> to, String from, {String subject:null, String message:null, DateTime datetime:null, HashMap<String, List<String>> meta:null, List<Attachment> attachments:null})
get this error:
Uncaught NoSuchMethodError: incorrect number of arguments passed to method named ''
Receiver: ""
Tried calling: (Instance of 'JSArray<String>', "will#fallenreaper.com", Instance of '_HashMap<String, Object>')
Found: (to, from, subject, message, datetime, meta, attachments)
My class is:
class Email{
Email( List<String> to, String from, {String subject:null, String message:null, DateTime datetime:null, HashMap<String, List<String>> meta:null, List<Attachment> attachments:null}){
//do stuff.
}
}
im trying to make it such that to and from are required, but the rest are optionally going to be passed in, in a map. I thought i was doing this right, but it doesnt seem to be correct.
The DartPad is at: https://dartpad.dartlang.org/4d32b88095a6509da511
Search for TODO
The Composer class is the part im implementing, leveraging the Email class i created.
Add some text to the Subject, and then click the "Send" button

Answer 1

Your Email class' constructor
Email( List<String> to, String from, {String subject:null, String message:null, DateTime datetime:null, HashMap<String, List<String>> meta:null, List<Attachment> attachments:null}) { ... }
has 2 positional arguments and 5 optional named arguments.
You can simply pass positional parameters like you did in
new Email(map["to"], map["from"], map);
but optional names parameters need to be "named" like
new Email(map["to"], map["from"], subject: map);
If you want the optional parameters to be positional you need to change the constructor to
Email( List<String> to, String from, [String subject=null, String message=null, DateTime datetime=null, HashMap<String, List<String>> meta=null, List<Attachment> attachments=null]) { ... }
You can't have optional named and optional positional arguments at the same time. If you have a longer parameter list like in your Email constructor, named optional arguments are usually better because you can specify with a name which parameter the passed value should be assigned to and there is no need to pass nulls or ''s for parameters you want to skip.