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class MainActivity : AppCompatActivity() {
  private var toolBar: Toolbar? = null
  private var container: ViewGroup? = null

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    coordinatorLayout {
      fitsSystemWindows = true

      appBarLayout {

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interface ViewBinder<in T> {
    fun bind(t: T) : View
    fun unbind(t: T)
}

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class MainLayout : ViewBinder<MainActivity> {

  override fun bind(mainActivity: MainActivity): View =
    mainActivity.UI {
      coordinatorLayout {
        fitsSystemWindows = true

        appBarLayout {
          mainActivity.toolBar = toolbar {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) elevation = 4f

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configuration(orientation = Orientation.LANDSCAPE, smallestWidth = 700) {
  recyclerView {
    init()
  }.lparams(width = widthProcent(50), height = matchParent)
  
  frameLayout().lparams(width = matchParent, height = matchParent)
}

fun <T : View> T.widthProcent(procent: Int): Int =
  getAppUseableScreenSize().x.toFloat().times(procent.toFloat() / 100).toInt()

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public class MainActivity extends AppCompatActivity {

    LinearLayout container;
    RecyclerView recycView;
    FrameLayout detailContainer;
    
    private MainLayout mainLayout = new MainLayout();

    @Override
    protected void onCreate(Bundle savedInstanceState) {

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sealed class MathExpression

data class Add(val left: MathExpression, val right: MathExpression) : MathExpression()
data class Sub(val left: MathExpression, val right: MathExpression) : MathExpression()
data class Number(val value: Int): MathExpression()

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sealed class MathExpression {
    abstract fun eval(): Int
}

data class Addition(val left: MathExpression, val right: MathExpression) : MathExpression() {
    override fun eval(): Int = left.eval() + right.eval()
}

data class Subtraction(val left: MathExpression, val right: MathExpression) : MathExpression() {
    override fun eval(): Int = left.eval() - right.eval()

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sealed class MathExpression {
        fun eval(): Int = when(this) {
        is Addition -> left.eval() + right.eval()
        is Subtraction -> left.eval() - right.eval()
        is Number -> value
    }
}

data class Addition(val left: MathExpression, val right: MathExpression) : MathExpression() 
data class Subtraction(val left: MathExpression, val right: MathExpression) : MathExpression()

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╔═══════════════════╦═════════════════════════╦═════════════════════════╗
║                   ║ Add new method          ║ Add new data            ║
╠═══════════════════╬═════════════════════════╬═════════════════════════╣
║ Polymorpish       ║ Change existing code    ║ Existing code unchanged ║
║ Pattern matching  ║ Existing code unchanged ║ Change existing code    ║
╚═══════════════════╩═════════════════════════╩═════════════════════════╝

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sealed class MathExpression {
    fun eval(): Int = when (this) {
        is Addition -> left.eval() + right.eval()
        is Subtraction -> left.eval() - right.eval()
        is Division -> left.eval() / right.eval()
        is Number -> value
    }
}

data class Addition(val left: MathExpression, val right: MathExpression) : MathExpression()