What is the best way to define types for an array of objects with interconnected properties?

Question

What is the best way to define types for an array of objects with interconnected properties?

I need to define a type for an object called root, which holds a nested array of objects called values. Each object in the array has properties named one (of any type) and all (an array of the same type as one).

Below is my attempt at creating this type declaration. However, I am unsure how to specify the type for the one property, so currently I have used just Value<any>:

type Value<T> = { one: T, all: T[] }
type Root = { values: Value<any>[] }

const root: Root = {
    values: [
        { one: 1, all: 5 }, // This should throw an error since 'all' should be an array of numbers.
        { one: true, all: [5] }, // This should also throw an error as 'all' should be an array of booleans.
        { one: 'a', all: ['a', 'b', 'c'] }, // Okay.
        { one: true, all: [false, true, true] } // Okay.
    ]
}

Is there a way to achieve this without explicitly listing all possible combinations of types like in this example? It would be great if it could work for any type without specifying them individually.

typescript generics

Answer 1

Answer №1

Upon observation, it's evident that the Root value is too broad to uphold the specific constraint you're interested in. However, it remains simple and straightforward to utilize:

const root: Root = {
    values: [
        { one: true, all: [5] }, // no error
        { one: 'a', all: ['a', 'b', 'c'] }, // good
        { one: true, all: [false, true, true] } // acceptable
    ]
}

const indexes = root.values.map(v => v.all.indexOf(v.one));
console.log(indexes) // [-1, 0, 1]

The above code snippet serves as a basis for comparison. Implementing the following approach will enforce the constraint, albeit at the cost of added complexity:

When you feel the need to define an infinite union type like the example below

type SomeValue = Value<string> | Value<number> | Value<boolean> 
  | Value<null> | Value<Date> | Value<{a: string, b: number}> | ...

it indicates a requirement for existentially quantified generic types. Languages with generics typically support universally quantified types, akin to intersection types. The feature request for existentially quantified generics is still pending in TypeScript.

An alternative method involves emulating these generics by switching the roles of data supplier and consumer. This allows for encoding SomeValue as follows:

type SomeValue = <R>(cb: <T>(value: Value<T>) => R) => R;

To access the underlying Value<T> data from a value someValue, a callback cb must be provided. An aiding function toSomeValue can transform any Value<T> into a SomeValue. This enables creating root with enforced type checking.

Furthermore, by incorporating additional complexities, such as making Root generic itself or mapping array types to Value<T>, one may achieve more flexible structures but at the expense of increased intricacy.

For further details and implementation examples, refer to the code within the referenced link.

Answer 2

Upon observation, it's evident that the Root value is too broad to uphold the specific constraint you're interested in. However, it remains simple and straightforward to utilize:

const root: Root = {
    values: [
        { one: true, all: [5] }, // no error
        { one: 'a', all: ['a', 'b', 'c'] }, // good
        { one: true, all: [false, true, true] } // acceptable
    ]
}

const indexes = root.values.map(v => v.all.indexOf(v.one));
console.log(indexes) // [-1, 0, 1]

The above code snippet serves as a basis for comparison. Implementing the following approach will enforce the constraint, albeit at the cost of added complexity:

When you feel the need to define an infinite union type like the example below

type SomeValue = Value<string> | Value<number> | Value<boolean> 
  | Value<null> | Value<Date> | Value<{a: string, b: number}> | ...

it indicates a requirement for existentially quantified generic types. Languages with generics typically support universally quantified types, akin to intersection types. The feature request for existentially quantified generics is still pending in TypeScript.

An alternative method involves emulating these generics by switching the roles of data supplier and consumer. This allows for encoding SomeValue as follows:

type SomeValue = <R>(cb: <T>(value: Value<T>) => R) => R;

To access the underlying Value<T> data from a value someValue, a callback cb must be provided. An aiding function toSomeValue can transform any Value<T> into a SomeValue. This enables creating root with enforced type checking.

Furthermore, by incorporating additional complexities, such as making Root generic itself or mapping array types to Value<T>, one may achieve more flexible structures but at the expense of increased intricacy.

For further details and implementation examples, refer to the code within the referenced link.

Answer 3

Answer №2

When considering your particular scenario, T may take on various forms such as a string, number, or boolean. Therefore, using it is not advisable.
A better approach would be to implement something similar to the following:

type Value = number | string | boolean
type ValueObject = { one: Value; all: Value[] }
type Root = { values: ValueObject[] }

Answer 4

When considering your particular scenario, T may take on various forms such as a string, number, or boolean. Therefore, using it is not advisable.
A better approach would be to implement something similar to the following:

type Value = number | string | boolean
type ValueObject = { one: Value; all: Value[] }
type Root = { values: ValueObject[] }

Answer 5

Answer №3

Simply put, the answer is no; I am doubtful that achieving what you intend to do is possible. Furthermore, it is advisable not to attempt it.

One potential approach for storing type information could be structured as follows:

const root: Root = {
    values: [
        { one: 1, all: 5 } as Value<number>, // This should trigger an error, as 'all' ought to be an array of numbers.
        { one: true, all: [5] } as Value<boolean>, // This should prompt an error too, with 'all' expected to be an array of booleans.
        { one: 'a', all: ['a', 'b', 'c'] } as Value<string>, // Acceptable.
        { one: true, all: [false, true, true] } as Value<boolean> // Acceptable.
    ]
}

However, envisioning a scenario where processing root.values involves looping without requiring conditionals seems challenging:

const process = (root) => {
  switch(typeof root) {
    case "number":
      ...
      break
    case "string":
      ...
      break
    case "boolean":
      ...
      break
  }

}

An alternative strategy would involve simplifying the procedure by substituting root with something akin to:

const intRoots: Value<number>[]
const boolRoots: Value<boolean>[]
const strRoots: Value<string>[]

Afterwards, handle each type explicitly without necessitating type checking: const ***Roots.map(...)

A guiding principle I often rely on (though it may have exceptions) is that if managing types during my processing poses challenges, reconsidering the data structure might prove beneficial.

Answer 6

Simply put, the answer is no; I am doubtful that achieving what you intend to do is possible. Furthermore, it is advisable not to attempt it.

One potential approach for storing type information could be structured as follows:

const root: Root = {
    values: [
        { one: 1, all: 5 } as Value<number>, // This should trigger an error, as 'all' ought to be an array of numbers.
        { one: true, all: [5] } as Value<boolean>, // This should prompt an error too, with 'all' expected to be an array of booleans.
        { one: 'a', all: ['a', 'b', 'c'] } as Value<string>, // Acceptable.
        { one: true, all: [false, true, true] } as Value<boolean> // Acceptable.
    ]
}

However, envisioning a scenario where processing root.values involves looping without requiring conditionals seems challenging:

const process = (root) => {
  switch(typeof root) {
    case "number":
      ...
      break
    case "string":
      ...
      break
    case "boolean":
      ...
      break
  }

}

An alternative strategy would involve simplifying the procedure by substituting root with something akin to:

const intRoots: Value<number>[]
const boolRoots: Value<boolean>[]
const strRoots: Value<string>[]

Afterwards, handle each type explicitly without necessitating type checking: const ***Roots.map(...)

A guiding principle I often rely on (though it may have exceptions) is that if managing types during my processing poses challenges, reconsidering the data structure might prove beneficial.

What is the best way to define types for an array of objects with interconnected properties?

Answer №1

Answer №2

Answer №3

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