CODEWITHSUNDEEP
kotlintype-inference
oshai
oshai

Reputation: 15365

How to tell that an extension method returns non-null if subject is not null

I have implemented the following method:

private fun String?.replaceHolder(item: String): String? {
  return this?.replace("\$deployUnit", item)
}

The code that is using it looks like that:

val a = "aaa".replaceHolder("fff")

However, the inferred type of a is String?. With contracts I can say that if the return value is not null then subject was is not null like that:

@ExperimentalContracts
private fun String?.replaceHolder(item: String): String? {
  contract {
    returnsNotNull() implies (this@replaceHolder != null)
  }
  return this?.replace("\$deployUnit", item)
}

Is it possible to say the opposite? I mean to infer that the type of a is not null? Is there another way to do that?

Upvotes: 3

Views: 308

Answers (1)

codegames
codegames

Reputation: 1921

if i understand you well this is what you want

private fun <T: String?> T.replaceHolder(item: String): T {
    return this?.replace("\$deployUnit", item) as T
}

T extends String? means that T type can be String or null or both and every type T is, function return that type too

Upvotes: 4

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