I was just astonished to find out that Map.getValue(key) does not guarantee non-null value. If a map...

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[Uziel Sulkies]

I was just astonished to find out that Map.getValue(key) does not guarantee non-null value.
If a map has explicit null value for a key, this method will return null !

Map getValue can return null!

[Uziel Sulkies]

Untitled

Untitled

[diesieben07]

Yes, null is still a value in the map.

[Uziel Sulkies]

Hmmm...
Now I understand that this if the map's type is <String, String?> the compiler treats the value as nullable.
The problem is when a json map with null value is deserialized into Map<String, String> which is not type-safe.
Then you can bypass the compiler's protection, and get an exception only when you try to something with the value, like using it as a constructor parameter of a non-nullable value.
Then you'll get exception in Runtime.

[diesieben07]

Yes, generics are erased. This is not limited to nullability. You can unsafely cast Map<String, Any> to Map<String, String> and then get an exception at runtime when you try to use the values as strings.

[arekolek]

The problem is when a json map with null value is deserialized into Map<String, String> which is not type-safe.

I’ve seen that problem with Gson. On the other hand moshi-kotlin works with non-nullable types properly.

[arekolek]

Although I’m not sure how that’s going to work with Map 🤔