英文:
Spreading tuples and also applying optional attributes
问题
以下是修改后的代码：
type ArrayBuilder<
T extends Def[],
A extends any[] = [],
B extends any[] = [],
C extends any[] = [],
State extends 'A' | 'B' = 'A',
> = T extends [
infer H extends Def,
...infer R extends Def[],
] ? State extends 'A' ? H['spread'] extends true ? ArrayBuilder<R, A, H['optional'] extends true ? [boolean] : [], [...A, H['type']], 'B'> : ArrayBuilder<R, [...A, H['type']], [], [], 'A'>
: ArrayBuilder<R, A, H['optional'] extends true ? [boolean] : [], [...C, H['type']], 'B'>
: [...A, ...B, ...C]
type Test2 = ArrayBuilder<[A, B, C]> // [string, boolean?, ...string[]]
通过在适当的位置添加条件来检查 optional 字段，我们可以实现 Test2 产生 [string, boolean?, ...string[]] 的结果。这里的条件检查将在需要时将 boolean 类型添加到类型数组中。
英文:
Can the code below be modified, such that Test2 produces: [string, boolean?, ...string[]] by factoring in the optional field?
type Def = { type: any, spread: boolean, optional: boolean }
type A = { type: string, spread: false, optional: false }
type B = { type: boolean, spread: false, optional: true }
type C = { type: string[], spread: true, optional: false }
type D = { type: number, spread: false, optional: false }
type ArrayBuilder<
T extends Def[],
A extends any[] = [],
B extends any[] = [],
C extends any[] = [],
State extends 'A' | 'B' = 'A',
> = T extends [
infer H extends Def,
...infer R extends Def[],
] ? State extends 'A' ? H['spread'] extends true ? ArrayBuilder<R, A, H['type'], [], 'B'> : ArrayBuilder<R, [...A, H['type']], [], [], 'A'>
:ArrayBuilder<R, A, B, [...C, H['type']], 'B'>
: [...A, ...B, ...C]
type Test1 = ArrayBuilder<[A,C,D]> // [string, ...string[], number]
// Can the code above be modified, such that Test2 produces: [string, boolean?, ...string[]] by factoring in the optional field?
type Test2 = ArrayBuilder<[A,B,C]> // [string, boolean, ...string[]] - should become [string, boolean?, ...string[]]
To apply the spread, I'm doing [...A,...ItemToSpread], but to apply the optional attribute I must do {[I in keyof T]?: T[I] } - which doesn't play nice with spreads.
答案1
得分: 2
正如你检查H["spread"]一样，你可以在将H["type"]传递给ArrayBuilder之前检查H["optional"]：
type ArrayBuilder<
T extends Def[],
A extends any[] = [],
B extends any[] = [],
C extends any[] = [],
State extends "A" | "B" = "A"
> = T extends [infer H extends Def, ...infer R extends Def[]]
? State extends "A"
? H["spread"] extends true
? ArrayBuilder<R, A, H["type"], [], "B">
: H["optional"] extends true ? ArrayBuilder<R, [...A, H["type"]?], [], [], "A"> : ArrayBuilder<R, [...A, H["type"]], [], [], "A">
: H["optional"] extends true ? ArrayBuilder<R, A, B, [...C, H["type"]?], "B"> : ArrayBuilder<R, A, B, [...C, H["type"]], "B">
: [...A, ...B, ...C];
如果你启用了exactOptionalPropertyTypes，你将获得Test2的期望结果：
type Test2 = ArrayBuilder<[A, B, C]>; // [string, boolean?, ...string[]]
英文:
Just as you check for H["spread"], you can check for H["optional"] before passing H["type"] to ArrayBuilder:
type ArrayBuilder<
T extends Def[],
A extends any[] = [],
B extends any[] = [],
C extends any[] = [],
State extends "A" | "B" = "A"
> = T extends [infer H extends Def, ...infer R extends Def[]]
? State extends "A"
? H["spread"] extends true
? ArrayBuilder<R, A, H["type"], [], "B">
: H["optional"] extends true ? ArrayBuilder<R, [...A, H["type"]?], [], [], "A"> : ArrayBuilder<R, [...A, H["type"]], [], [], "A">
: H["optional"] extends true ? ArrayBuilder<R, A, B, [...C, H["type"]?], "B"> : ArrayBuilder<R, A, B, [...C, H["type"]], "B">
: [...A, ...B, ...C];
and if you have exactOptionalPropertyTypes enabled, you will get the desired result for Test2:
type Test2 = ArrayBuilder<[A, B, C]>; // [string, boolean?, ...string[]]
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