Expected an compiler error, but it didn't came :wi...

# compiler

[Peter]

Expected an compiler error, but it didn't came 😉

Is this expected behavior?

class Dummy {

    // Define as read-only access map
    private val buffers: Map<String, String>

    init {
        buffers = mutableMapOf()

        // Unexpected, no error
        buffers["test"] = "hello"
    }

    fun dummy2() {

        // Not allowed, as expected
       buffers["test"] = "hello"
    }

}

[ephemient]

I think it's just smart casting, works in a local function too:

fun main() {
    val buffers: Map<String, String>
    buffers = mutableMapOf()
    buffers["test"] = "hello"
}

[Peter]

I agree it is smart casting at work. I'm just not convinced smart casting should be done at assignment. Seems to break some common OO patterns of using abstractions like interfaces instead of implementations.

Another side effect is that the below two snippets behave differently, which might come as a surprise.

// Works 
val buffers: Map<String, String>
buffers = mutableMapOf()
buffers["test"] = "hello"

// Error
val buffers2: Map<String, String> = mutableMapOf()
buffers2["test"] = "hello"