KtMap.map(MapEntry<K, V> -> R) : KtList<R>

[passsy]

Kotlin allows mapping of entries in a map using .map

mapOf(1 to "foo", 2 to "bar")
        .map { "${it.key} -> ${it.value}" }
        .forEach(::print)
// 1 -> foo
// 2 -> bar

This leads to a name clash with KtMap.map which returns the Dart Map.

Currently all kt.dart collections allow access to the dart equivalents.

KtIterable.iter -> Iterable
KtList.list -> List
KtMap.map -> Map
KtSet.set -> Set

We have to find a way to provide standardized ways to access the dart equivalents. Additionally we should make it as easy as possible to make kt.dart collections useable using for loops.

// kt.dart 0.5.0
for(final i in listOf(1, 2, 3).iter) {
  print(i);
}

[passsy]

One way of solving it would be to convert the interop properties to functions called asMap(), asList(), asSet() and asList().

But this would clash with the existing KtIterable<T>.asIterable(): KtIterable<T>

And for loops would look even worse

for(final i in listOf(1, 2, 3).asIterable()) {
  print(i);
}

[passsy]

We could keep iter but create functions for all the others. iter is the only usage where a short name is useful. for is the only dart language construct which works directly with a collection.

KtIterable.iter -> Iterable
KtList.asList() -> List
KtMap.asMap() -> Map
KtSet.asSet() -> Set

[passsy]

On could name the map function mapEntries and avoid naming collisions

[passsy]

mapEntries() wouldn't be a great solution because it wouldn't be consistent with mapNotNull()

[christoph-jerolimov]

From other languages I would expect that KtMap.map is a mapping function similar to your first Kotlin example, and exactly what the title of this issue describes. This is also the behaviour in the Dart List:

void main() {
  [1, 2, 3, 4, 5]
    .map((i) => i * 2)
    .forEach(print);
}

I would prefer another (new?) naming convention to get the standard Dart objects from the Kt* objects. I would renamed them to asList, asMap, ... or toList, toMap.

I didn't yet understand the problem with asIterable. Why is this required in this example? Shouldn't the KtList implements Iterable already?

for(final i in listOf(1, 2, 3).asIterable()) {
  print(i);
}

[passsy]

Context why KtList does not implement Iterable and instead offers a .iter property.
https://github.com/dart-lang/language/issues/226

[christoph-jerolimov]

Okay, thanks for the context. I understand now that the Iterable interface is much bigger than expected..

With this step back, I didn't see a big point why a map method is needed. Esp. mapping over a map is always a little bit tricky. Are the code maps over the key or values or both?

Readable code is so important, that I think its also great that KtMap has already the options to map over the keys, values and entries with KtMap.keys, KtMap.values and KtMap.entries. Or? Maybe you can push the documentation or example into this direction and show the benefits of this.

mapFrom({ "a": 1, "b": 2, "sum": 3 })
  .entries
  .filter((entry) => entry.key != "sum")
  .map((entry) => entry.value)
  .map((value) => value * 2)
  .forEach(print);

Hopefully you will get some other feedback as well. For me, I'm fine with the current version. 😏