covariant method
Assert that JavaScript's x
is the proper type represented by this
Type.
Implementation
@override
bool covariant(x) {
// `>=` because tuples can be covariant when encoded.
return ((x is List) &&
x.length >= _fields.length &&
_components.asMap().entries.map((t) {
return t.value.covariant(x[t.key]) ? 0 : 1;
}).reduce((value, element) => value + element) ==
0);
}