i have a setter method: `fromJson(JsonToObjectMapp...

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[tipsy]

i have a setter method: fromJson(JsonToObjectMapper jsonToObjectMapper) (java), which configures how my library does json-mapping:

public interface JsonToObjectMapper {
    <T> T map(String json, Class<T> targetClass);
}

calling this method works fine from java, but kotlin is unable to infer types. if i try to to:

val gson = GsonBuilder().create()
myPlugin.fromJson(gson::fromJson)

i just get None of the following functions can be called with the arguments supplied.

any ideas?

[Andreas Sinz]

@tipsy JsonToObjectMapper is a kotlin interface, right?

[tipsy]

i've tried both java and kotlin, java gets me bit farther (the one i pasted here is java)

[Andreas Sinz]

if you define the interface in java, you can try myPlugin.fromJson { json, cls -> gson.fromJson(json, cls) }

[Andreas Sinz]

i don't think SAM conversion works with gson::fromJson

[Andreas Sinz]

https://kotlinlang.org/docs/reference/java-interop.html#sam-conversions

[tipsy]

yeah, and you can't have lambdas with generics

[tipsy]

😞

[Andreas Sinz]

does JsonToObjectMapper only have a single method?

[tipsy]

yes

[Andreas Sinz]

you could use a function type instead of an interface:

typealias JsonToObjectMapper<T> = (String, Class<T>) -> T

fun MyPlugin.fromJson(map: JsonToObjectMapper<T>) {
    ....
}

[Andreas Sinz]

then you can use any function that has the same shape, e. g. myPlugin.fromJson(gson::fromJson) works

[tipsy]

i believe this will work fine from kotlin, but not java

[Andreas Sinz]

it should work just fine (if kotlin-stdlib is included in the java project), function types are just functional interfaces

[tipsy]

alright, i'll give it a try, thanks

[tipsy]

Type inference failed: Not enough information to infer parameter T in 

fun <T> fromJson(map: JsonToObjectMapper<T> /* = (String, Class<T>) → T */): Unit

[tipsy]

worked in java though, so that's good