(#1572) Covariance for `func.FuncWithFallback`

DmitryBarskov commented 3 years ago

For #1572:

Generify ScalarWithFallback (generify this class since FuncWithFallback depends on it)
Generify FuncWithFallback

Now fallbacks for ScalarWithFallback and FuncWithFallback can produce object derived types from given original type.

Fallback<Long> longOnNoFile = new Fallback.From<>(FileNotFoundException.class, _t -> 0L);
Fallback<Double> doubleOnIo = new Fallback.From<>(IOException.class, _t -> 0.0);
Fallback<Integer> intOtherwise = new Fallback.From<>(Exception.class, _t -> 0);

Func<String, Number> readFileLength = new FuncOf<>(fileName -> {
  throw new IOException("Access denied. You can't read file " + fileName);
});

FuncWithFallback<String, Number> safeReadFileLength =
  new FuncWithFallback<String, Number>(
    readFileLength,
    longOnNoFile,
    doubleOnIo,
    intOtherwise
  );