Add KeyPath and PathValue types

[kainiedziela]

Fixes #147

Playground link

KeyPath

Represents a dot path to a nested object property.

Use case: to be used in any helper function that extracts values based on a string dot path, like lodash.get or dot-prop.

PathValue

Targets a property from a nested object using a dot path.

Use case: Extracting a given value from a complex API requests that is otherwise non-essential outside that value.

Example

declare function get<T, P extends KeyPath<T>>(obj: T, path: P): PathValue<T, P>;
const user = {
  firstName: 'Foo',
  lastName: 'Bar',
  projects: [
    { name: 'Baz', contributors: 68 },
    { name: 'Waldo', contributors: 12 },
  ]
};

get(user, 'projects.0.name');

[sindresorhus]

I did you see #153 ?

[kainiedziela]

I did not. Makes this obsolete I guess.

[sindresorhus]

Yeah, sorry. It was first so I'm going to go with that. Would be great if you could help review #153.