Language Feature: Parallel Assignment

[DartBot]

This issue was originally filed by @simonpai

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Maybe it's possible to support parallel assignment like in Ruby and Python. For example:

// return domain, port,
(String, int) parseURL(String url) { ... }

String domain;
int port;
(domain, port) = parseURL('http://dart.com:9999'); // gets domain = 'dart.com', port = 9999

or even more elegantly:

(String domain, int port) = parseURL('http://dart.com:9999');

Dart should be able to keep the all type information in compile time, so it has benefit over returning an unparametrized List. But I am not sure how many effort it takes to implement this.

This is not a must-have feature, but shall come in handy when you need it.

[jmesserly]

Removed Type-Defect label.
Added Type-Enhancement, Area-Language, Triaged labels.

[jmesserly]

Added Duplicate label.
Marked as being merged into #75.