E9020 Array Errors
unusable-as-map-key
type cannot be used as map key
When this occurs
Using a non-hashable type (array, map, struct) as a map key
Example error message
error[E9020]:
type 'array' cannot be used as map key
How to fix
Map keys must be hashable types: `string`, `int`, `float`, `bool`, or `char`. Convert the value to a hashable type.