带推理的Typescript模板字面值

Question

代码约定用'$'标记一个实体的子实体(=与另一个实体的关联)。

class Pet {
owner$: any;
}

当引用子实体时，应该允许用户使用完整的表单('owner$')或更简单的表单('owner')。

我正在尝试这样的结构:

type ChildAttributeString = `${string}$`;
type ShortChildAttribute<E> = ((keyof E) extends `${infer Att}$` ? Att : never);
type ChildAttribute<E> = (keyof E & ChildAttributeString) | ShortChildAttribute<E>;
const att1: ChildAttribute<Pet> = 'owner$'; // Valid type matching
const att2: ChildAttribute<Pet> = 'owner'; // Valid type matching
const att3: ChildAttribute<Pet> = 'previousOwner$'; // Invalid: previousOwner$ is not an attribute of Pet - Good, this is expected

只要Pet的所有属性都是子属性，这就可以工作，但是一旦我们添加了一个非子属性，匹配就会中断:

class Pet {
name: string;
owner$: any;
}
const att1: ChildAttribute<Pet> = 'owner$'; // Valid type matching
const att2: ChildAttribute<Pet> = 'owner'; // INVALID: Type 'string' is not assignable to type 'never'
// To be clear: ChildAttribute<Pet> should be able to have these values: 'owner', 'owner$'
// but not 'name' which is not a child (no child indication trailing '$')

什么是合适的类型呢?

——编辑

我不清楚预期结果和"实体子"的定义，因此发布了答案，所以我编辑了问题以使其更清楚。

Answer 1

这里我们映射键:如果一个键以$结尾，我们包括完整和简短的形式，否则我们省略它:

type ValuesOf<T> = T[keyof T]
type ChildAttribute<E> = 
ValuesOf<{ [K in keyof E]: K extends `${infer Att}$` ? K | Att : never }>
interface Pet {
name: string
owner$: any
}
type PetAttr = ChildAttribute<Pet> // "owner$" | "owner"

Answer 2

ChildAttribute应该返回所有允许的值的并集。

type RemoveDollar<
T extends string,
Result extends string = ''
> =
(T extends `${infer Head}${infer Rest}`
? (Rest extends ''
? (Head extends '$' ? Result : `${Result}${Head}`) : RemoveDollar<Rest, `${Result}${Head}`>) : never
)
// owner
type Test = RemoveDollar<'owner$'>

据我所知，如果值是$，我们可以应用短getter，但如果属性没有$，如name，我们不能使用name$作为getter。

如果我的假设是正确的，这个解决方案应该适用于你:

interface Pet {
name: string;
owner$: any;
}

type RemoveDollar<
T extends string,
Result extends string = ''
> =
(T extends `${infer Head}${infer Rest}`
? (Rest extends ''
? (Head extends '$' ? Result : `${Result}${Head}`) : RemoveDollar<Rest, `${Result}${Head}`>) : never
)
// owner
type Test = RemoveDollar<'owner$'>
type WithDollar<T extends string> = T extends `${string}$` ? T : never
// owner$
type Test2 = WithDollar<keyof Pet>
type ChildAttribute<E> = keyof E extends string ? RemoveDollar<keyof E> | WithDollar<keyof E> : never
const att1: ChildAttribute<Pet> = 'owner$'; // Valid type matching
const att2: ChildAttribute<Pet> = 'owner'; // Valid type matching
const att3: ChildAttribute<Pet> = 'previousOwner$'; // Invalid: previousOwner$ is not an attribute of Pet - Good, this is expected

游乐场

递归

type RemoveDollar<
T extends string,
Result extends string = ''
> =
(T extends `${infer Head}${infer Rest}`
? (Rest extends ''
? (Head extends '$' ? Result : `${Result}${Head}`) : RemoveDollar<Rest, `${Result}${Head}`>) : never
)
/**
* First cycle
*/
type Call = RemoveDollar<'foo$'>
type First<
T extends string,
Result extends string = ''
> =
// T extends        `{f}         {oo$}
(T extends `${infer Head}${infer Rest}`
? (Rest extends '' // Rest is not empty
// This branch is skipped on first iteration         
? (Head extends '$' ? Result : `${Result}${Head}`)
// RemoveDollar<'oo$', ${''}${f}>
: RemoveDollar<Rest, `${Result}${Head}`>
) : never
)
/**
* Second cycle
*/
type Second<
T extends string,
// Result is f
Result extends string = ''
> =
// T extends       `{o}$         {o$}
(T extends `${infer Head}${infer Rest}`
? (Rest extends '' // Rest is not empty
// This branch is skipped on second iteration         
? (Head extends '$' ? Result : `${Result}${Head}`)
// RemoveDollar<'o$', ${'f'}${o}>
: RemoveDollar<Rest, `${Result}${Head}`>
) : never
)
/**
* Third cycle
*/
type Third<
T extends string,
// Result is fo
Result extends string = ''
> =
// T extends       `{o}          {$}
(T extends `${infer Head}${infer Rest}`
? (Rest extends '' // Rest is not empty, it is $
// This branch is skipped on third iteration         
? (Head extends '$' ? Result : `${Result}${Head}`)
// RemoveDollar<'$', ${'fo'}${o}>
: RemoveDollar<Rest, `${Result}${Head}`>
) : never
)
/**
* Fourth cycle, the last one
*/
type Fourth<
T extends string,
// Result is foo
Result extends string = ''
> =
// T extends       `${$}        {''}
(T extends `${infer Head}${infer Rest}`
? (Rest extends '' // Rest is  empty
// Head is $           foo   
? (Head extends '$' ? Result : `${Result}${Head}`)
// This branch is skipped on last iteration
: RemoveDollar<Rest, `${Result}${Head}`>
) : never
)

游乐场