Why is using a wrongly typed index into a Map not an error but just a warning

[escamoteur]

I got bitten by this here

_imageCache is defined

  final Map<ReactionType, ui.Image> _imageCache = {};

where ReatcionType is an enum.
The warning says: The argument type 'String' isn't related to 'ReactionType'

even with

analyzer:
  language:
    # strict-casts: true
    # strict-inference: true

it stays a warning that throws an exception at runtime. I think this should always be treated as an error. Which use case would make sense to allow code with this to compile?

[dart-github-bot]

Summary: The user is reporting that accessing a Map with a wrongly typed index (e.g., using a String key when the Map expects a ReactionType enum) only generates a warning, not an error, even with strict type checking enabled. They believe this should be an error to prevent runtime exceptions and are asking for justification for allowing this behavior.

[lrhn]

The API of Map gives the operator [] the signature K operator[](Object? key).

It does that for a number of reasons, but mainly that you can cast a of, fx, Map<int, String> to, fx, Map<num, String> and still use it, and, fx, do numMap[3.14] without getting a type error.

The same argument applies to a number of operations:

• Iterable.contains
• List.remove
• Set.remove
• Set.lookup
• Set.intersection
• Set.difference
• Set.containsAll
• Set.removeAll
• Set.retainAll
• Map.containsKey
• Map.containsValue
• Map.operator[]
• Map.remove

All of these operations can work on objects that are a supertype of the element/key/value type, because they don't require the input to become an element/key/value. They just ask if there is one that's equal to it, and "no" is a fine answer.

It's deliberate and not something that is easy to change at this point, even if there was something good to change it to.

[escamoteur]

But as the Linzer is able to detect it, why not default it to error? Am 15. Nov. 2024, 21:29 +0100 schrieb Lasse R.H. Nielsen ***@***.***>:

…

The API of Map gives the operator [] the signature K operator[](Object? key). It does that for a number of reasons, but mainly that you can cast a of, fx, Map<int, String> to, fx, Map<num, String> and still use it, and, fx, do numMap[3.14] without getting a type error. The same argument applies to a number of operations: • Iterable.contains • List.remove • Set.remove • Set.lookup • Set.intersection • Set.difference • Set.containsAll • Set.removeAll • Set.retainAll • Map.containsKey • Map.containsValue • Map.operator[] • Map.remove All of these operations can work on objects that are a supertype of the element/key/value type, because they don't require the input to become an element/key/value. They just ask if there is one that's equal to it, and "no" is a fine answer. It's deliberate and not something that is easy to change at this point, even if there was something good to change it to. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.Message ID: ***@***.***>