I have a nullability question: this works but Kotlin thinks that the return value could be "T" inste...

# getting-started

[Stephan Schröder]

I have a nullability question: this works but Kotlin thinks that the return value could be "T" instead of "T?".

inline fun <reified T : Any> RestTemplate.getForObject(path: String): T? {
    return this.getForObject(path, T::class.java)
}

but the RestTemplate.getForObject is a nullable Java function:

@Nullable
    public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException {

Is this a type inference bug/confusion?

[Sam]

It works as expected for me — I get a warning if I try to return T, and no warning if I follow the suggestion to change it to T?. What versions of Spring/Kotlin/IntelliJ are you using?

[Stephan Schröder]

good to hear it works as expected on your machine!
Spring: 2.7.12
Kotlin: 1.9.0
JVM: 17
IntelliJ: 2023.2 Build #IU-232.8660.185, built on July 26, 2023

[xoangon]

A generic type T can be nullable in Kotlin. Using T? is redundant, so I can figure that's the reason for the warning

[Michael de Kaste]

that would be true, but T has been specified to be T : Any

[Sam]

Even if T isn’t specified as non-null, T and T? are still different. Unbounded T is maybe-nullable, and T? is definitely-nullable.

[xoangon]

Oh you're right. I wasn't seeing that upper Any bound

[Michael de Kaste]

@Stephan Schröder I have the same as @Sam, perhaps some issues with intellijs caching and whatnot, try clearing them

[Stephan Schröder]

this morning there was an IntelliJ update to 2023.2.1 and now the wrong warning is gone 🙂