Why is possible to write a function outside a class in Kotlin?

Question

I don\'t understand why is possible to write a function outside a class in Kotlin ? Is that a good practice ?

For example, it\'s possible in Kotlin to write a funct

Answer 1

Yes, it is a good practice to create package-level functions if the function logic is independent of properties and lifecycle of a class. Example:

• a function to convert miles per gallon to kilometers per litre is independent of any object and fits well as package-level.
• otoh, a function to cancel reservation would naturally be associated with a specifc reservation object and fits well inside such a class.

The main benefit of a package-level function is simplicity (ergo better maintainability): callers of your function don't need to declare and create an object to call the function. (If your package-level function needs to be called from Java code, this benefit is lost because the Java calling code has to use a class name that is generated by Kotlin.)

IMPORTANT: Although you don't have a class lexical scope for your function, the Single-Responsibility Principle (SRP) still applies. Do not create a Kotlin source file, say Util.kt, and bloat it up with functions that lack cohesion, that is, functions that do unrelated things.