See: https://twitter.com/HandstandSam/status/1350096311098503168

ImmutableDataWithMutableStateFlowTest.kt

package com.handstandsam.mutablestateflow

import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.test.runBlockingTest
import org.junit.Test

class UseImmutableDataWithMutableStateFlow {

    data class SomePojo(var name: String = "placeholder")

    @Test
    fun testMutableDataIsBad() = runBlockingTest {
        val somePojo = SomePojo()
        val mutableStateFlow = MutableStateFlow(somePojo)
        println("INITIAL: ${mutableStateFlow.value}")

        // Update the value
        somePojo.name = "Something Different"

        // Assign the new value to the MutableStateFlow

        println("CURRENT: ${mutableStateFlow.value}")
        mutableStateFlow.value = somePojo
        println("UPDATED: ${mutableStateFlow.value}")
        
        // It's the same object you already modified and therefore the value is the same,
        // and no emission will occur from the MutableStateFlow 
    }
}

output.txt

INITIAL: SomePojo(name=placeholder)
CURRENT: SomePojo(name=Something Different)
UPDATED: SomePojo(name=Something Different)

Thanks very much for this