Result<T>

Result<T> is the central error-handling primitive of functional-reactive. Think of it as Optional<T> with a reason for the absence.

Result<User> user = repository.findById(id);

user.ifPresentOrElse(
    u   -> log.info("Found {}", u),
    err -> log.warn("Lookup failed: {}", err)
);

Construction

Method	Description
`Result.success(t)`	Wraps a non-null value.
`Result.failure(reason)`	Marks the absence of a value with a message.
`Result.ofNullable(t)`	Success if non-null, otherwise failure.
`Result.fromOptional(opt)`	Bridge from `java.util.Optional`.

Transformations

map(Function) — transform the value if present.
flatMap(Function<T, Result<U>>) — chain another Result-returning operation.
or(Supplier) — fall back to another Result.

Combinators

thenCombine(value, BiFunction) — combine with a plain value.
thenCombineAsync(value, BiFunction) — same, but asynchronous.

Terminal operations

ifPresent(Consumer) / ifAbsent(Runnable) / ifFailed(Consumer<String>)
ifPresentOrElse(Consumer, Consumer<String>)
stream() — zero-or-one element stream.
toOptional() — back to java.util.Optional.

When to reach for Result

Use Result whenever absence has a reason the caller cares about — failed parsing, missing config, lookups that may fail. Reach for Optional when absence is the entire information.