feat(option): introduce option component

[azjezz]

Signed-off-by: azjezz azjezz@protonmail.com

[coveralls]

Pull Request Test Coverage Report for Build 3554950291

• 37 of 37 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 98.977%

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Totals
Change from base Build 3554915568:	0.04%
Covered Lines:	3386
Relevant Lines:	3421

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💛 - Coveralls

[veewee]

Looks nice!

[Ocramius]

Just cross-linking here: I've provided a full example @ https://gist.github.com/Ocramius/368bd78c38cc5bb857e931801f6e4af7

Beware that Optional is not necessarily OptionalField.

• Optional in Java attempted to abstract T|null (because Java sucks at handling null - it's so so bad!).
• in my example, I attempt to abstract T|null|absent, where absent, which is a slightly different problem 👍

[azjezz]

forPossiblyMissingArrayKey

I was thinking with the addition of Option, we could add the following functions to Dict and Vec components, which would implement basically that.

Dict\get<Tk, Tv>(dict<Tk, Tv> $d, Tk $k): Option<Tv> {
  return Iter\contains_key($d, $k) ? Option\some($d[$k]) : Option\none();
}

Dict\get_typed<T>(dict<array-key, mixed> $d, array-key $k, Type\TypeInterface<T> $t): Option<T> {
  return Iter\contains_key($d, $k) ? Option\some($t->coerce($d[$k])) : Option\none();
}

Vec\get<T>(vec<T> $v, int $k): Option<T> {
  return Iter\contains_key($v, $k) ? Option\some($v[$k]) : Option\none();
}

Vec\get_typed<T>(vec<mixed> $v, int $k, Type\TypeInterface<T> $t): Option<T> {
  return Iter\contains_key($v, $k) ? Option\some($t->coerce($v[$k])) : Option\none();
}

[azjezz]

in my example, I attempt to abstract T|null|absent, where absent, which is a slightly different problem 👍

To note, null is a valid "Some" in this implementation of Option, where Option\some(null)->isNone() is false, it's up to you to create a "none" in case of null if that is what you desire.

[veewee]

Discussed the open topics in this PR with @azjezz. There is nothing blocking that is stopping us from merging and releasing this PR. We can always take in additional improvements once people start using this component and start seeing better ways to do things.