and also, i've upgraded for kotlin 1.3 to 1.4 and noticed some smart casts to string have broken; is...

# getting-started

[xii]

and also, i've upgraded for kotlin 1.3 to 1.4 and noticed some smart casts to string have broken; is doing toString in the original object sufficient, or does smart cast do something I'm not taking into account?

[corneil]

How about an example of the failing code?

[xii]

of course:

data class Test(
  val otherValue: Instant
  val nullableMap: Map<String,String>? = null
)

class TestClass(){
  fun previouslyFineFunction(foo: Test){
    val body = mutableMapOf(
      "otherValue" to foo.otherValue
    )
    if (foo.nullableMap != null){
       body["baz"] = foo.nullableMap
    }
  }
}

[xii]

previously the

body["baz"] = foo.nullableMap

worked straight up

[Klitos Kyriacou]

Isn't the right-hand side of that assignment supposed to be an Instant?

[xii]

no, it's a mutable map of <String, Any>

[xii]

previously, my IDE would say

Smart cast to kotlin.collections.Map<kotlin.String, kotlin.String>

on the body["baz"] line

[xii]

but now it doesnt do it by itself

[Klitos Kyriacou]

Yes, it still smart-casts foo.nullableMap to Map<kotlin.String, kotlin.String> since it knows it's not null. But that's not where the problem is. You can't put a Map as a value into a Map that was initialized with an Instant as a value. If you really want to do that, you have to be explicit about its type when you create it:

val body : Map<String, Any> = mutableMapOf(...)

[xii]

hmmm

[xii]

the error i get from 1.4 forwards is

[xii]

Type mismatch.
Required:
Comparable<{Instant & String}>
Found:
Map<String, String>
Type mismatch.
Required:
Serializable
Found:
Map<String, String>
Type mismatch.
Required:
{Comparable{Instant & String}> & java.io.Serializable}
Found:
Map<String, String>

[xii]

but you are right in that if I specify <String, Any> it behaves as it used to

[Klitos Kyriacou]

The inferred type of body depends on the contents of the MutableMap that you initialize it with. For the compiler to give the above error message, you must have initialized it with:

val body = mutableMapOf(
            "otherValue" to foo.otherValue,
            "xyz" to "abc",
        )

and not just with "otherValue" to foo.otherValue. The inferred type it chooses is the most restrictive type that matches all of the arguments to mutableMapOf. If you gave it another type, which was totally different from these two, then it would have to infer the map type as Map<String, Any>. For example, if you did this:

val body = mutableMapOf(
            "otherValue" to foo.otherValue,
            "xyz" to listOf(123)
        )

then your code would work.

[xii]

yep, very interesting! thank you! 🙂