#31997 - Parameter Intersection (#31998)

Co-authored-by: David Blass <[email protected]>

questions/31997-extreme-parameter-intersection/README.md

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+Given two parameter arrays, compute a third tuple representing the type of args required to satisfy both of the original tuples.
+
+Your solution should correctly handle fixed and non-fixed length arrays, optional elements and variadic elements. For example:
+
+```ts
+type Result = IntersectParameters<
+ [{ a: 0 }, { b: 1 }?, { c: 2 }?, ...{ d: 3 }[]],
+ [{ e: 4 }?, { f: 5 }?, ...{ g: 6 }[]]
+>
+
+type Expected = [
+ {
+ a: 0
+ e: 4
+ },
+ {
+ b: 1
+ f: 5
+ }?,
+ {
+ c: 2
+ g: 6
+ }?,
+ ...{
+ d: 3
+ g: 6
+ }[]
+]
+```

questions/31997-extreme-parameter-intersection/info.yml

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+difficulty: extreme
+title: Parameter Intersection
+tags: parameters, array, variadic, optional, rest, intersection
+author:
+ github: ssalbdivad
+ name: David Blass
+

questions/31997-extreme-parameter-intersection/template.ts

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+type IntersectParameters<
+ l extends readonly unknown[],
+ r extends readonly unknown[]
+> = l & r

questions/31997-extreme-parameter-intersection/test-cases.ts

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+import type { Equal, Expect } from "@type-challenges/utils"
+
+type result1 = IntersectParameters<[], []>
+type TwoEmpty = Expect<Equal<[], result1>>
+
+type result2 = IntersectParameters<[], [string, number, ...boolean[]]>
+type OneEmpty = Expect<Equal<[string, number, ...boolean[]], result2>>
+
+type result3 = IntersectParameters<["a"], [string, number]>
+type LongerParametersPreserved = Expect<Equal<["a", number], result3>>
+
+type result4 = IntersectParameters<[unknown], []>
+// Avoids evaluating unknown to {}
+type UnknownPreserved = Expect<Equal<[unknown], result4>>
+
+type result5 = IntersectParameters<[("a" | "b" | "c")?], [string, 1 | 2 | 3]>
+type OneOptional = Expect<Equal<["a" | "b" | "c", 1 | 2 | 3], result5>>
+
+type result6 = IntersectParameters<[{ a: 0 }?], [{ b: 1 }?]>
+type BothOptional = Expect<Equal<[{ a: 0; b: 1 }?], result6>>
+
+type result7 = IntersectParameters<[{ a: 0 }?], []>
+type OptionalAndNotPresent = Expect<Equal<[{ a: 0 }?], result7>>
+
+type result8 = IntersectParameters<{ a: 0 }[], { b: 1 }[]>
+type TwoNonFixedLength = Expect<Equal<{ a: 0; b: 1 }[], result8>>
+
+type result9 = IntersectParameters<[{ a: 0 }, { b: 1 }], { c: 2 }[]>
+type OneNonFixedLength = Expect<
+ Equal<
+ [
+ {
+ a: 0
+ c: 2
+ },
+ {
+ b: 1
+ c: 2
+ },
+ ...{
+ c: 2
+ }[]
+ ],
+ result9
+ >
+>
+
+type result10 = IntersectParameters<
+ [{ a: 0 }, ...{ b: 1 }[]],
+ [{ c: 2 }, { d: 3 }]
+>
+type OneTrailingRest = Expect<
+ Equal<
+ [
+ {
+ a: 0
+ c: 2
+ },
+ {
+ b: 1
+ d: 3
+ },
+ ...{
+ b: 1
+ }[]
+ ],
+ result10
+ >
+>
+
+type result11 = IntersectParameters<
+ [{ a: 0 }, ...{ b: 1 }[]],
+ [{ c: 2 }, { d: 3 }, ...{ e: 4 }[]]
+>
+type TwoTrailingRest = Expect<
+ Equal<
+ [
+ {
+ a: 0
+ c: 2
+ },
+ {
+ b: 1
+ d: 3
+ },
+ ...{
+ b: 1
+ e: 4
+ }[]
+ ],
+ result11
+ >
+>
+
+type result12 = IntersectParameters<
+ [{ a: 0 }, { b: 1 }?, { c: 2 }?, ...{ d: 3 }[]],
+ [{ e: 4 }?, { f: 5 }?, ...{ g: 6 }[]]
+>
+type KitchenSink = Expect<
+ Equal<
+ [
+ {
+ a: 0
+ e: 4
+ },
+ {
+ b: 1
+ f: 5
+ }?,
+ {
+ c: 2
+ g: 6
+ }?,
+ ...{
+ d: 3
+ g: 6
+ }[]
+ ],
+ result12
+ >
+>
+
+type result13 = IntersectParameters<["a", "b"], [string, ...string[]]>
+type ExtraVariadicArgsPreserved = Expect<
+ Equal<["a", "b", ...string[]], result13>
+>