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Chainable options

MediumP2Coding

Implement the Chainable type for an options builder.

declare const config: Chainable
const result = config.option('foo', 123).option('name', 'x').get()
  • option(key, value) returns a new chainable whose accumulated object type has key: typeof value added.
  • get() returns the accumulated object type.
  • Using a key that was already set is a type error.
  • The resulting object type must be one flat object type, not an intersection.

Tests your type must pass

declare const config: Chainable

const result1 = config
  .option('foo', 123)
  .option('name', 'type-challenges')
  .option('bar', { value: 'Hello World' })
  .get()

const result2 = config.option('a', true).get()

const result3 = config.get()

interface Result1 {
  foo: number
  name: string
  bar: { value: string }
}

type cases = [
  Expect<Equal<typeof result1, Result1>>,
  Expect<Equal<typeof result2, { a: boolean }>>,
  Expect<Equal<typeof result3, {}>>,
]

// @ts-expect-error the key 'foo' is already set
config.option('foo', 1).option('foo', 2)

Hints

TypeScript
Run and Submit type-check your solution against the tests.