Add Extension methods to strings and others

[feinstein]

It would be nice to convert methos such as isBlank("myString") to "myString".isBlank, using the new Extension methods from Dart 2.7.

[feinstein]

@cbracken I am willing to add the extensions, but extensions are only supported on Dart 2.6 and this will break quiver's compatibility with older project.

Thoughts?

[fabiancrx]

I would like having them as extension methods. I think auto completion and commodity will be enhanced.

[cbracken]

Sorry it took a while to notice this -- agreed, I think this would be a nice feature.

Quiver is currently backward compatible to Dart SDK 2.0.0-dev.61 so this would be considered a breaking change and we'd need to bump our major version to 3.0.0. Given that non-null by default is also on its way, what I might do is create a 3.0.0-dev branch that we can commit things like this to and publish dev releases from to pub. Seem reasonable?

[cbracken]

/cc @jtmcdole @yjbanov for thoughts on the branch strategy. This is pretty much the approach we took with Dart 2.0 and I feel like that worked about as well as could be expected given the extent of those changes (which reminds me... there are still some method stubs we haven't finished implementing).

[feinstein]

@cbracken I like it. Let me know when it's done so I can add the extensions.

[cbracken]

Branch 3.0.0-dev has now been created.

[feinstein]

@cbracken I am almost done, I just want to confirm with you how do you prefer the tests to be structured.

I am placing them all together under strings_test.dart, so if someone changes one test doesn't forget to update another file as well.

But I am not sure how to expand the tests.

For example, here's one test:

test('should consider empty string a blank', () {
  expect(isBlank(''), isTrue);
});

I can convert this to:

1:

test('should consider empty string a blank', () {
  String s = '';
  expect(isBlank(s), isTrue);
  expect(s.isBlank, isTrue);
});

or

2:

test('should consider empty string a blank', () {
  expect(isBlank(''), isTrue);
  expect(''.isBlank, isTrue);
});

2 is easier to do and I also find 2 easier to read, but 1 is more maintainable, as we can change the string once and all the tests will reflect it.

Do you have any particular preference? I started the file as 1 already, but on loop tests I am finding it a bit uglier.