A series of functions with designated return types passed to the subsequent function

Question

A series of functions with designated return types passed to the subsequent function

I have a vision to craft an innovative array that is filled with functions.

const a = [
  (): { a: string } => ({ a: 'alpha'}),
  ({ a }): { b: string } => ({ b: 'beta' }),
  ({ a, b }): {} => ({}),
]

The functions are specified with return types, but I desire a method to eliminate the need for specifying input types and instead generate a "chaining" mechanism where all inputs are merged into the return types of previous functions in the sequence.

If achieving this directly isn't feasible, could I at least implement an interface like the following:

interface State {
  a: string,
  b: string
}

And potentially formulate a generic type for the array that utilizes State as a partial application to both input and output types for each function within the array?

typescript

Answer 1

Answer №1

To establish a sequence of functions where each function relies on the output of the preceding one, you must define a function and overloads for every number of functions you wish to accommodate:

function chain<R1, R2, R3, R4>(fn1: ()=> R1, fn2: (a: R1) => R2, fn3: (a: R1 & R2) => R3, fn4: (a: R1 & R2 & R3) => R4) : [typeof fn1, typeof fn2, typeof fn3, typeof fn4]
function chain<R1, R2, R3>(fn1: ()=> R1, fn2: (a: R1) => R2, fn3: (a: R1 & R2) => R3) : [typeof fn1, typeof fn2, typeof fn3]
function chain<R1, R2>(fn1: ()=> R1, fn2: (a: R1) => R2) : [typeof fn1, typeof fn2]
function chain(...fns: Array<(a?: any)=> any>) : Array<(a?: any)=> any> {
    return fns;
}

const a =chain( // return types are not necessary.
    () => ({ a: 'alpha'}),
    ({ a })  => ({ b: 'beta' }),
    ({ a, b }) => ({ c: a, z:a }),
)

Answer 2

To establish a sequence of functions where each function relies on the output of the preceding one, you must define a function and overloads for every number of functions you wish to accommodate:

function chain<R1, R2, R3, R4>(fn1: ()=> R1, fn2: (a: R1) => R2, fn3: (a: R1 & R2) => R3, fn4: (a: R1 & R2 & R3) => R4) : [typeof fn1, typeof fn2, typeof fn3, typeof fn4]
function chain<R1, R2, R3>(fn1: ()=> R1, fn2: (a: R1) => R2, fn3: (a: R1 & R2) => R3) : [typeof fn1, typeof fn2, typeof fn3]
function chain<R1, R2>(fn1: ()=> R1, fn2: (a: R1) => R2) : [typeof fn1, typeof fn2]
function chain(...fns: Array<(a?: any)=> any>) : Array<(a?: any)=> any> {
    return fns;
}

const a =chain( // return types are not necessary.
    () => ({ a: 'alpha'}),
    ({ a })  => ({ b: 'beta' }),
    ({ a, b }) => ({ c: a, z:a }),
)

Answer 3

Answer №2

Not the best solution, but it does provide some level of support:

type TransformationFn<T> = (input: Partial<T>) => Partial<T> | Promise<Partial<T>>;
type Transformations<T> = TransformationFn<T>[]

interface Data {
  foo: string,
  bar: string
}

const transformations: Transformations<Data> = [
  () => ({ foo: 'value1'}),
  ({ foo }) => ({ bar: 'value2' }),
  ({ foo, bar }): {} => ({}),
]

Answer 4

Not the best solution, but it does provide some level of support:

type TransformationFn<T> = (input: Partial<T>) => Partial<T> | Promise<Partial<T>>;
type Transformations<T> = TransformationFn<T>[]

interface Data {
  foo: string,
  bar: string
}

const transformations: Transformations<Data> = [
  () => ({ foo: 'value1'}),
  ({ foo }) => ({ bar: 'value2' }),
  ({ foo, bar }): {} => ({}),
]

A series of functions with designated return types passed to the subsequent function

Answer №1

Answer №2

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