Add "builtAt" to builders

[davidmorgan]

ListBuilder could for example have a "builtAt" method that converts the value at the specified index to a builder, similar to the "rebuild" method but for an element in the collection:

var list = new BuiltList<BuiltList>([new BuiltList[1]]);
var rebuiltList = list.rebuild((b) => b.rebuildAt(0).add(2));

--> [[1, 2]]

This should work for nested built collections and for built values.

[sroddy]

any hope for having this implemented any time soon? :)

[davidmorgan]

Last I looked at this, it required a lot of boilerplate to make it work--because you have to tell the collection the type of the builder that it needs to expose.

It's possible that with Dart 2's type inference this can be workable. I'll take a look again sometime. But probably not very soon ;) ... the next changes for built_collection will be improvements related to Dart 2.

[neckaros]

Any news on this?

[davidmorgan]

It's actually possible to do this with extension methods now :)

I've been waiting to see how the simpler extension methods (build, toBuiltList, toBuiltSet, toBuiltMap) are received. They seem to have gone smoothly.

[brandondiamond]

Another enthusiastic dev -- this would clean up a bunch of my code.

[davidmorgan]

You can actually do this yourself now using extension methods :) I've explored adding them, but didn't get around to a final answer yet. If you try it I'd be interested to hear how it goes :)

Something like this:

extension BuiltValueListBuilderExtension<V extends Built<V, B>,
    B extends Builder> on ListBuilder<Built<V, B>> {
  void rebuildAt(int index, void Function(B) updates) =>
      this[index] = this[index].rebuild(updates);
}

extension BuiltValueMapBuilderExtension<K, V extends Built<V, B>,
    B extends Builder> on MapBuilder<K, Built<V, B>> {
  void rebuildAt(K key, void Function(B) updates) =>
      this[key] = this[key].rebuild(updates);
}

[neckaros]

Thanks!
here is the slightly modified working version:

extension BuiltValueListBuilderExtension<V extends Built<V, B>,
    B extends Builder<V, B>> on ListBuilder<Built<V, B>> {
  void rebuildAt(int index, void Function(B) updates) =>
      this[index] = this[index].rebuild(updates);
}

extension BuiltValueMapBuilderExtension<K, V extends Built<V, B>,
    B extends Builder<V, B>> on MapBuilder<K, Built<V, B>> {
  void rebuildAt(K key, void Function(B) updates) =>
      this[key] = this[key].rebuild(updates);
}

i'm trying to do a rebuildWhere as it would greatly reduce the number of line of code in my async "Bloc" update process (need to get the current index often to avoid edition of the wrong index if list changed). but i don't see how yet. will post back here if find a way. But since ListBuilder doesn't expose indexWhere it won't be easy i think :)

[davidmorgan]

How about something like

for (var i = 0; i != this.length; ++i) {
  if (condition(this[i])) this[i] = this[i].rebuild(updates);
}

?

[neckaros]

So simple yet working 👍

Thanks!!!

[kushvatsa]

Hey @davidmorgan , rebuildAt working 👍 . Thank you!!

[shubhamtanwar23]

@kushvatsa I think this will work

extension BuiltValueListBuilderExtension<V extends Built<V, B>,
    B extends Builder<V, B>> on ListBuilder<Built<V, B>> {

  void rebuildWhere(bool Function(V) test, void Function(B) updates) {
    for (var i = 0; i != this.length; ++i) {
      if (test(this[i])) this[i] = this[i].rebuild(updates);
    }
  }
}

[kushvatsa]

It works @shubhamtanwar23 , Thank you 👍

[smkhalsa]

@davidmorgan is there anything preventing one of the above solutions from being merged in?

[davidmorgan]

@smkhalsa Nothing specific :) I'm a little hesitant about adding extension methods, since they're new, and once they're added it's a breaking API change to change them. Also, it's easy to roll your own :D

I'll look at adding these in a coming release.

[arlucio]

How do I use these extension methods?

I'm trying to use them but I'm not sure where to add them so that they are recognized.

Tried to use it like I use any other extension methods: Creating a file with them and trying to import that file whenever I need to use the methods (like below), but they are not recognized.

import 'package:built_collection/built_collection.dart';
import 'package:built_value/built_value.dart';

extension BuiltValueListBuilderExtension<V extends Built<V, B>, B extends Builder<V, B>> on ListBuilder<Built<V, B>> {
  void rebuildAt(int index, void Function(B) updates) => this[index] = this[index].rebuild(updates);
}

var list = BuiltList<BuiltList>([BuiltList.from([1])]);
var rebuiltList = list.rebuild((b) => b.rebuildAt(0).add(2));

In this "rebuildAt" is not recognized as an option. How to use this?

[davidmorgan]

You're calling

rebuildAt(0).add(2)

it should be

rebuildAt(0, (b) => b..add(2))

:)