/**
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Convert a union type to an intersection type using [distributive conditional types](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#distributive-conditional-types).
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Inspired by [this Stack Overflow answer](https://stackoverflow.com/a/50375286/2172153).
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@example
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```
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import {UnionToIntersection} from 'type-fest';
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type Union = {the(): void} | {great(arg: string): void} | {escape: boolean};
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type Intersection = UnionToIntersection<Union>;
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//=> {the(): void; great(arg: string): void; escape: boolean};
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```
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A more applicable example which could make its way into your library code follows.
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@example
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```
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import {UnionToIntersection} from 'type-fest';
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class CommandOne {
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commands: {
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a1: () => undefined,
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b1: () => undefined,
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}
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}
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class CommandTwo {
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commands: {
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a2: (argA: string) => undefined,
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b2: (argB: string) => undefined,
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}
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}
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const union = [new CommandOne(), new CommandTwo()].map(instance => instance.commands);
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type Union = typeof union;
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//=> {a1(): void; b1(): void} | {a2(argA: string): void; b2(argB: string): void}
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type Intersection = UnionToIntersection<Union>;
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//=> {a1(): void; b1(): void; a2(argA: string): void; b2(argB: string): void}
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```
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*/
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export type UnionToIntersection<Union> = (
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// `extends unknown` is always going to be the case and is used to convert the
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// `Union` into a [distributive conditional
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// type](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#distributive-conditional-types).
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Union extends unknown
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// The union type is used as the only argument to a function since the union
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// of function arguments is an intersection.
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? (distributedUnion: Union) => void
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// This won't happen.
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: never
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// Infer the `Intersection` type since TypeScript represents the positional
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// arguments of unions of functions as an intersection of the union.
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) extends ((mergedIntersection: infer Intersection) => void)
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? Intersection
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: never;
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