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Implicit error when trying to implement the `Absurd` typeclass

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问题 I'm trying to implement the Absurd typeclass (as seen in Haskell's Data.Boring library) in Scala. I'm able to define an Absurd instance for Nothing . Unfortunately, when I try to define an absurd instance for Either , I get a missing implicit error sealed trait Absurd[A] { def absurd[X](a: A): X } object Absurd { def apply[A: Absurd, B](a: A):B = implicitly[Absurd[A]].absurd[B](a) implicit val absurdForNothing: Absurd[Nothing] = new Absurd[Nothing]{ override def absurd[X](a: Nothing): X = a }

Implicit error when trying to implement the `Absurd` typeclass

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What means in Dart static type and why it differs with runtime type?

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问题 In Dart exists two kind of types. Runtime type Static type Here is proof in Dart language specification: The static type of null is bottom. Runtime type of null is Null Static type of null is bottom This mean that objects in Dart can have two kind of types. One real type that called static and one virtual type that called runtime . That is, runtime type of null is not a bottom but a regular class Null . class Null { factory Null._uninstantiable() { throw new UnsupportedError('class Null

BottomNavigationView not showing in my activity

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问题 I am implementing BottomNavigationView using this link i implemented everything step by step but my navigationview not showup at bottom of the screen. this is what i done. public class MainActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback { Intent intent = null; BottomNavigationView navigationView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);

BottomNavigationView not showing in my activity

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I am implementing BottomNavigationView using this link i implemented everything step by step but my navigationview not showup at bottom of the screen. this is what i done. public class MainActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback { Intent intent = null; BottomNavigationView navigationView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); navigationView = (BottomNavigationView) findViewById(R.id.navigation); navigationView