Dart and underscores

Question

I decided to implement the functional underscore.js library in Dart.

I wrote the functions in 'underscore.dart' with some example functions shown below:

library underscore;

List _filter (ff, List s) => return s..retainWhere(ff);

List _dropWhile(ff,List s) => s.skipWhile(ff).toList();

In my main Dart program, I then added the import statement

import 'underscore.dart';

However, I got the persistent error on that line of 'Unused Import', and so none of the functions were recognised.

It did work, though, when I redefined 'underscore.dart' as 'part of mainProg' and made 'mainProg' a library in its own right.

Further testing shows that it is the underscores on the function names that is causing the problem.

Any ideas?

Answer 1

A prepending underscore means that the function is library private. That is, you can't use it in an other library. See Libraries and Visibility.

Libraries not only provide APIs, but are a unit of privacy: identifiers that start with an underscore (_) are visible only inside the library.