final allows to avoid accidentaly reassign a local variable and prevents bugs.

Personnally I would never enable unnecessary_final in one of my project.

See also https://stackoverflow.com/a/316787/634863

Thanks @a14n .

We have fans of both approaches--as on that stackoverflow answer. In google3 it looks like >50% prefers var to final, although it's not overwhelming.

With this lint, the linter can now enforce whichever of the two you like, or neither :)

My personal interest is to try to make the tools good enough that nobody wants final for locals. The IDE could highlight local variable reassignments for you; there's no need for you to do it by hand.

My personal interest is to try to make the tools good enough that nobody wants final for locals.

I find this idea confusing. IMO the value of final is in communicating intent (that the tools can then use to help keep you on the rails). I don't understand why we'd ever want to do away with that.

Unlike Java final can be used to introduce variable in Dart.

It looks like the benefits of using final are rarely challenged. The main concern on the Java side is that it adds verbosity:

// in java
String s = "";
// with java>=11
final var s = "";
//--- with final
final String s = "";
// with java>=11
final var s = "";

In Dart the difference is smaller (so the main drawback is lowered):

// in java
var s = '';
// with java>=11
final s = '';

We've had this discussion a lot of times internally :)

Originally I was on the side of final. I'd like it to be the default in the language, but since it isn't, we could at least add it manually everywhere. So, I argued for everyone to use it everywhere.

People didn't want to :) ... they argued that the extra typing (just two characters, but in lots of places) doesn't add enough value. Eventually, after raising this topic repeatedly over a number of years, I figured it's never going to happen: we can't make final the standard since Dart was created with var.

So I changed my own code to use var. e.g. here was the change for built_value: google/built_value.dart@7ea8681

And my personal experience is that it makes no difference whatsoever. I can't think of a single case where using var instead of final caused me problems. And it is, indeed, two characters shorter, which is nice.

I hope that one day either enforcement of final or enforcement of not using final we be added to package:pedantic, resolving the issue one way or the other. However, since I have to get a consensus for either change, and the current split is pretty close to fifty fifty, this may unfortunately be an uphill struggle :)

One more thought. Enforcing this lint has the nice property that it makes final just for fields, and var just for locals. That cuts down on confusion about what final does/means, and aids readability overall.

Thanks.