Assigning a default value if one doesnt exist in enum

Support
1

I wanted to know if it was possible to set a default value for a enum class if a value doesn’t exist in the class.

So if a enum class looked like →
enum class Example { EXAMPLE1, EXAMPLE2, EXAMPLE3, EXAMPLE4 }
and I say a value calls for Example.EXAMPLE5 is there a way I can default it to have a value of Example.EXAMPLE1?

2

I’m not sure exactly what you mean by that. Do you mean a function that takes an argument of type Example?

fun foo(example: Example)

In that case you can use default arguments

fun foo(example: Example = Example.EXAMPLE1)

If this isn’t what you mean, can you show a code example of what your code looks like now and where you want the default value?

3

You can’t just make a static call like Example.EXAMPLE5, because it simply won’t compile. In case of executing out-of-date Jar it will throw some kind of runtime error when parsing the bytecode.

The only sensible example I could think of would be a data parsing like with Jackson, JAXB, etc. If you want to avoid null values you could then use default values or Null Object pattern depending on your case.

4

Are you thinking of data parsing? Like, Example.valueOf("EXAMPLE5")?

In that case, you have the same options to handle this situation as in Java:

  • You could wrap it in a try { ... } catch { ... } and handle undefined/invalid values one way or the other (i.e. returning null then)

      fun parseExample(str: String): Example? {
      return try {
          Example.valueOf(str)
      } catch(e: IllegalArgumentException) {
          null
      }

  • You could check beforehand if the input string is EXAMPLE5 or anything other and do your custom thing.:

      fun parseExample(str: String): Example {
      return when(str) {
          "EXAMPLE5" -> Example.EXAMPLE1
          else -> Example.valueOf(str)
      }
  }
5

I assume you mean by calling Example.valueOf(“EXAMPLE5”), you want a default value instead of it throwing an exception.
My solution for this was to first create a general kotlin function that returns a default value in case of any error:

fun catchOrDefault(default: R, block: () → R) = try { block() } catch (e: Throwable) { default }

Then I could use it like this:

catchOrDefault(Example.EXAMPLE1) { PushType.valueOf(“EXAMPLE5”) }

1 Like