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oamaok/Option.ts

Last active March 11, 2021 11:28
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Option.ts
type OptionValue<T> = [] | [T];
type OptionMethods<T> = {
map<A>(fn: (v: T) => A): Option<A>;
filter(fn: (v: T) => boolean): Option<T>;
chain<A>(fn: (v: T) => Option<A>): Option<A>;
exists(fn: (v: T) => boolean): boolean;
fold<A>(onNone: () => A, onSome: (v: T) => A): A;
alt(fn: () => Option<T>): Option<T>;
toNullable(): T | null;
isSome(): boolean;
};
type Option<T = any> = Pick<OptionValue<T>, never> & OptionMethods<T>;
class OptionImpl<T> extends Array<T> {
exists: OptionMethods<T>["exists"] = super.some;
fold: OptionMethods<T>["fold"] = (onNone, onSome) => {
if (this.length) return onSome(this[0]);
return onNone();
};
alt: OptionMethods<T>["alt"] = (fn) => {
if (this.length) return (this as unknown) as Option<T>;
return fn();
};
chain: OptionMethods<T>["chain"] = (fn) => {
if (this.length) return fn(this[0]);
return none;
};
toNullable: OptionMethods<T>["toNullable"] = () => {
if (this.length) return this[0];
return null;
};
isSome = () => this.length === 1;
}
function coerce<To>(value: any): To {
return (value as unknown) as To;
}
function some<T>(v: T): Option<T> {
return coerce<Option<T>>(new OptionImpl(v));
}
const none = coerce<Option>(new OptionImpl());
type OptionAllArgs<A, B, C, D, E, F> =
| [Option<A>, Option<B>]
| [Option<A>, Option<B>, Option<C>]
| [Option<A>, Option<B>, Option<C>, Option<D>]
| [Option<A>, Option<B>, Option<C>, Option<D>, Option<E>]
| [Option<A>, Option<B>, Option<C>, Option<D>, Option<E>, Option<F>];
type OptionAllRet<A, B, C, D, E, F> =
| Option<[A, B]>
| Option<[A, B, C]>
| Option<[A, B, C, D]>
| Option<[A, B, C, D, E]>
| Option<[A, B, C, D, E, F]>;
function all<A, B>(...args: [Option<A>, Option<B>]): Option<[A, B]>;
function all<A, B, C>(
...args: [Option<A>, Option<B>, Option<C>]
): Option<[A, B, C]>;
function all<A, B, C, D>(
...args: [Option<A>, Option<B>, Option<C>, Option<D>]
): Option<[A, B, C, D]>;
function all<A, B, C, D, E>(
...args: [Option<A>, Option<B>, Option<C>, Option<D>, Option<E>]
): Option<[A, B, C, D, E]>;
function all<A, B, C, D, E, F>(
...args: [Option<A>, Option<B>, Option<C>, Option<D>, Option<E>, Option<F>]
): Option<[A, B, C, D, E, F]>;
function all<A, B, C = never, D = never, E = never, F = never>(
...args: OptionAllArgs<A, B, C, D, E, F>
): OptionAllRet<A, B, C, D, E, F> {
switch (args.length) {
case 2: {
const [a, b] = args as [any, any];
if (a.length && b.length)
return coerce<Option<[A, B]>>(new OptionImpl([a[0], b[0]]));
return none;
}
case 3: {
const [a, b, c] = args as [any, any, any];
if (a.length && b.length && c.length)
return coerce<Option<[A, B, C]>>(new OptionImpl([a[0], b[0], c[0]]));
return none;
}
case 4: {
const [a, b, c, d] = args as [any, any, any, any];
if (a.length && b.length && c.length && d.length)
return coerce<Option<[A, B, C, D]>>(
new OptionImpl([a[0], b[0], c[0], d[0]])
);
return none;
}
case 5: {
const [a, b, c, d, e] = args as [any, any, any, any, any];
if (a.length && b.length && c.length && d.length && e.length)
return coerce<Option<[A, B, C, D, E]>>(
new OptionImpl([a[0], b[0], c[0], d[0], e[0]])
);
return none;
}
case 6: {
const [a, b, c, d, e, f] = args as [any, any, any, any, any, any];
if (a.length && b.length && c.length && d.length && e.length && f.length)
return coerce<Option<[A, B, C, D, E, F]>>(
new OptionImpl([a[0], b[0], c[0], d[0], e[0], f[0]])
);
return none;
}
}
}
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