Update code example for Instantiation to Bound Algorithm

[jmewes]

Observed

In the Dart language specification there the following code example for the section "Generics > Instantiation to Bound > The Instantiation to Bound Algorithm":

typedef Inv<X> = X Function(X);
class B<Y extends num, Z extends Inv<Y>> {}

B b; // The raw B means B<num, Inv<num>>.

(see 14efbe8/specification/dartLangSpec.tex#L8044-L8049)

This yields a not_initialized_non_nullable_variable error.

Expected

The variable b should have a nullable type, contain an instance of type B, or be declared within a function.

typedef Inv<X> = X Function(X);

class B<Y extends num, Z extends Inv<Y>> {
  Y? y;
  Z? z;
}

void main() {
  B b = B();
  assert(b.y is num?);
  assert(b.z is Inv<num>?);
}

Comment

In the example below there is a similar code snippet that shows an example for a compilation error. It might be useful to adapt this as well, so that it show the expected compilation error.

[eernstg]

Good catch, thanks! Handled in 8f1fd57.