map_key_type_not_assignable

The element type '{0}' can't be assigned to the map key type '{1}'.

The analyzer produces this diagnostic when a key of a key-value pair in a map literal has a type that isn't assignable to the key type of the map.

The following code produces this diagnostic because 2 is an int, but the keys of the map are required to be Strings:

var m = <String, String>{2 : 'a'};

If the type of the map is correct, then change the key to have the correct type:

var m = <String, String>{'2' : 'a'};

If the type of the key is correct, then change the key type of the map:

var m = <int, String>{2 : 'a'};

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.