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I'm attempting to implement parts of Mike Penz' NavigationDrawer (https://github.com/mikepenz/MaterialDrawer) in Kotlin. Since then I've run into only a few issues, primarily with operators. Here is part of the code to instantiate the drawer itself. Android Studio doesn't throw any errors except where I'm using the == operator on int and Long variables:

        // Create the Drawer
        result = DrawerBuilder()
                .withSliderBackgroundColor(ContextCompat.getColor(applicationContext, R.color.top_header))
                        PrimaryDrawerItem().withName(R.string.drawer_item_profile).withIcon(FontAwesome.Icon.faw_user).withIdentifier(1).withSelectable(false).withIconColor(ContextCompat.getColor(applicationContext, R.color.icon_grey)).withTextColor(ContextCompat.getColor(applicationContext, R.color.stroke)),
                        PrimaryDrawerItem().withName(R.string.drawer_item_create).withIcon(FontAwesome.Icon.faw_paint_brush).withIdentifier(2).withSelectable(false).withIconColor(ContextCompat.getColor(applicationContext, R.color.icon_grey)).withTextColor(ContextCompat.getColor(applicationContext, R.color.stroke)),
                        PrimaryDrawerItem().withName(R.string.drawer_item_yaanich_news).withIcon(FontAwesome.Icon.faw_newspaper_o).withIdentifier(3).withSelectable(false).withIconColor(ContextCompat.getColor(applicationContext, R.color.icon_grey)).withTextColor(ContextCompat.getColor(applicationContext, R.color.stroke)),
                        PrimaryDrawerItem().withName(R.string.drawer_item_my_groups).withIcon(FontAwesome.Icon.faw_users).withIdentifier(4).withSelectable(false).withIconColor(ContextCompat.getColor(applicationContext, R.color.icon_grey)).withTextColor(ContextCompat.getColor(applicationContext, R.color.stroke)),
                        PrimaryDrawerItem().withName(R.string.drawer_item_settings).withIcon(FontAwesome.Icon.faw_cog).withIdentifier(5).withSelectable(false).withIconColor(ContextCompat.getColor(applicationContext, R.color.icon_grey)).withTextColor(ContextCompat.getColor(applicationContext, R.color.stroke))
                .withOnDrawerItemClickListener { view, position, drawerItem ->

                    if (drawerItem != null) {
                        var intent: Intent? = null
                        if (drawerItem.identifier == (1) {
                            intent = Intent(this, UserProfileActivity::class.java)
                        } else if (drawerItem.identifier == 2) {
                            intent = Intent(this, YeetActivity::class.java)
                        } else if (drawerItem.identifier == 3) {
                            intent = Intent(this, RssActivity::class.java)
                        } else if (drawerItem.identifier == 4) {
                            intent = Intent(this, GroupsActivity::class.java)
                        } else if (drawerItem.identifier == 5) {
                            intent = Intent(this, UserSettingsActivity::class.java)
                        if (intent != null) {

        RecyclerViewCacheUtil<IDrawerItem<*, *>>().withCacheSize(2).apply(result!!.recyclerView, result!!.drawerItems)

        if (savedInstanceState == null) {
            result!!.setSelection(21, false)
            headerResult!!.activeProfile = profile


if (drawerItem.identifier == (1)

if (drawerItem.identifier == 2)

Operator == cannot be applied to 'Long and' 'Int'

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    • Unlike Java, Kotlin does not automatically promote numbers to wider types. You have to explicitly use the same types for these comparisons. Franscesc gave the correct answer, but if your int was stored in a variable, you would do if (drawerItem.identifier == id.toLong()).

Simply use long on your right side

if (drawerItem.identifier == 1L)

Edit: the reason this is required is that Kotlin does not promote Ints to Longs (or, more generally, does not widen types); on the left side we had a Long and on the right side we had an Int, which lead to the error. Explicitly indicating that the right side is a Long fixes the error.

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      • 2
    • The L explicitly casts declares the 1 as a Long type so they can be compared now. "Explicitly indicating that the right side is a Long fixes the error."
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    • How broadly true is the statement "Kotlin does not promote/widen types"? Other things do work, like ordered comparisons and the elvis operator. For example, if (someLongValue > 1) works (ditto >=, <, and <=), and someNullableLongValue ?: 0 works and has type Long.