Discussion on: How Interfaces May Eliminate Need For Pattern Matching (sometimes)

[Sergiy Yevtushenko]

It can be any function which may succeed or fail depending on conditions.

Following example is taken from real project code:

    private static Optional<Instant> parseInstantCursor(JSONObject params) {
        return safeString(params, "cursor")
            .toOptional()
            .flatMap(source -> Optional.of(source.split(":"))
                .filter(v -> v.length == 2)
                .flatMap(HighLevelApiHandler::parseInstant));
    }

    private static Optional<Instant> parseInstant(String[] pair) {
        return allOf(parseLong(pair[0]).filter(v -> v > 0), parseInt(pair[1]).filter(v -> v >= 0))
            .map(Instant::ofEpochSecond);
    }

    private static Optional<Long> parseLong(String input) {
        try {
            return Optional.of(Long.parseLong(input));
        } catch (NumberFormatException e) {
            return Optional.empty();
        }
    }

This example also shows how looks new coding style mentioned at the beginning of the article.