Why Kotlin does not allow slash in identifiers

Question

The Unicode is allowed in identifiers in backticks

val `💾id` = "1"

But slash is not allowed

val `application/json` = "application/json"

In Scala we can have such names.

Answer 1

This is a JVM limitation. From the specification section 4.2.2:

Names of methods, fields, local variables, and formal parameters are stored as unqualified names. An unqualified name must contain at least one Unicode code point and must not contain any of the ASCII characters . ; [ / (that is, period or semicolon or left square bracket or forward slash).

In Scala names are mangled to avoid this limitation, in Kotlin they are not.

Answer 2

Kotlin's identifiers are used as-is, without any mangling, in the names of JVM classes and methods generated from the Kotlin code. The slash has a special meaning in JVM names (it separates packages and class names). Therefore, Kotlin doesn't allow using it in an identifier.