yield_of_invalid_type

A yielded value of type '{0}' must be assignable to '{1}'.

The type '{0}' implied by the 'yield*' expression must be assignable to '{1}'.

The analyzer produces this diagnostic when the type of object produced by a yield or yield* expression doesn't match the type of objects that are to be returned from the Iterable or Stream types that are returned from a generator (a function or method marked with either sync* or async*).

The following code produces this diagnostic because the getter zero is declared to return an Iterable that returns integers, but the yield is returning a string from the iterable:

Iterable<int> get zero sync* {
  yield '0';
}

If the return type of the function is correct, then fix the expression following the keyword yield to return the correct type:

Iterable<int> get zero sync* {
  yield 0;
}

If the expression following the yield is correct, then change the return type of the function to allow it:

Iterable<String> get zero sync* {
  yield '0';
}