The Elvis operator - ?: - is nice because it lets you easily return something besides null: fun toUpper(s: String?): String = s?. I do that because the function accepts a nullable string, and may therefore return a null value: fun toUpper(s: String?): String? = s?.toUpperCase() Given the design of HashMap implementation in Java, you can have atmost one null vale as a key and multiple null values for one null key and multiple non null. In the previous lesson I returned String? from my toUpper function. returns null, but ?: lets you return some other value besides null

?: comes after a nullable type instance and can be read as “or else” or “if that’s null do this”.

A string is empty if it contains no characters Empty items are null. The official name for this operator is the “Null Coalescing Operator,” and I think “Elvis Operator” is just easier to remember. In React, map () can be used to generate lists. I don’t see it myself, but I’ve read that if you turn your head sideways the ?: characters look a little like Elvis. But what about those times where you want to handle that null value and return something besides null? That’s where the so-called “Elvis” Operator comes in. The Safe-Call operator shown in the previous lesson is nice in many situations where a variable may contain a null value, and you’re okay with ending up with another null value when you use it in an expression. Returns a list containing only the non-null results of applying the given transform function to each entry in the original map.

Kotlin map not null