Hi All, Need a little help with something I have b...

# android

[Ritwik Raj Srivastava]

Hi All, Need a little help with something I have been struggling since days.
Lets say I have a Extension function

fun Any?.toJSONString(): String {
  return this?.let {
    try {
      val gson = GsonBuilder().setPrettyPrinting().create()
      gson.toJson(this)
    } catch (e: Exception) {
      "{}"
    }
  } ?: "{}"
}

And I have another Extension function that takes in Generic T and I want to parse/manipulate the result. For example being

fun <T : Any> Response<MyResponse<T>>.toStr(): String {
  return T.toJSONString()
}

I am getting this error

Type parameter 'T' cannot have or inherit a companion object, so it cannot be on the left hand side of dot

Please help me out. If anyone can explain the error itself. It will be great. I do not have indepth Kotlin know-hows.

[Abhi]

what do you mean, T.toJSONString(), T is a bounded type here, it is not a variable of type T.

You can call toJSONString() on object instances of type "Any?".

[Abhi]

think about it, if you call T.toJSONString(), then what will "this" be in body of toJSONString()?

[Ritwik Raj Srivastava]

Thank you @Abhi for this great explanation. Got to learn something new.
Just to expand on it a bit. Is there no way to make an object from it.

[Abhi]

Your toStr() is an extension function on Response<MyResponse<T>>,

so in this toStr(), the "this" refers to an object of type Response<MyResponse<T>>

It depends on how you are using generics, without the definition of Response and MyResponse, one can't answer your question

[Ronald Wolvers]

Since this will in this case point to an object of type Response you will have to traverse down to the object of type T using functions defined on Response and on MyResponse as well. The type parameters on both would have to be marked out (covariant) though or not use variance, otherwise it's not possible - as far as I'm aware - to define a function that returns an object of the type that is the type parameter. For example, a List has a method get() which returns an object of the type that is its type parameter, and so you would need a function like that too for both Response and for `MyResponse`: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list/#kotlin.collections.List