feat(get): add get

[piquark6046]

Summary

This PR addresses #215 and #91 by implementing the get function.

Benchmark

[vercel]

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[de-novo]

@piquark6046 I would like to suggest an improvement to the types in this PR. The current issue is that when the path depth exceeds one level, the return type is inferred as unknown. It would be beneficial if the return value of the get function could be clearly inferred.

Below is a type example that addresses this issue. This is a type I have used personally, and while it may not work perfectly in all situations, it should serve as a useful reference.

type Split<STR extends string, SEP extends string> = string extends SEP
  ? string[]
  : STR extends `${infer A}${SEP}${infer B}`
    ? [A, ...(B extends '' ? [] : Split<B, SEP>)]
    : SEP extends ''
      ? []
      : [STR];

type ReplaceAll<T extends string, A extends string, B extends string> = T extends `${infer C}${A}${D}`
  ? `${C}${B}${ReplaceAll<D, A, B>}`
  : T;

export type StringPathToArray<T extends string> = Split<ReplaceAll<ReplaceAll<T, '[', '.'>, ']', ''>, '.'>;
type At<T extends object | any[], K extends Array<string | number>> = K extends [
  infer F extends string | number,
  ...infer R extends Array<string | number>,
]
  ? F extends keyof T
    ? AtHelper<T[F], R>
    : F extends `${infer N extends number}`
      ? N extends keyof T
        ? AtHelper<T[N], R>
        : never
      : never
  : T;

type AtHelper<T, R> = T extends object | any[] ? At<T, R> : T;
interface Test {
  a: { b: { c: number[] } };
}

type test = At<Test, ['a', 'b', 'c', 0]>; // number

interface Test2 {
  a: Array<{ b: { c: number[] } }>;
}

type test2 = At<Test2, ['a', 0, 'b', 'c']>; // number[]

[piquark6046]

@de-novo Can you please describe about D in your code snippet?

[raon0211]

Hey, thanks for your contribution!

We were in the process of working on the get function. Let me combine our version with the one you implemented.

[raon0211]

Hello @de-novo , thanks for your suggestion!

Unfortunately, one of our core values of our library is simple implementation. I understand that your provided type helps our type safety, but I guess the type is too complicated to merge. We might open a new issue about this.

Let me merge this pull request, and let's discuss about correct types in the other issue if needed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.49%. Comparing base (404d4a5) to head (95c5f54).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #232      +/-   ##
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+ Coverage   99.47%   99.49%   +0.01%     
==========================================
  Files          92       93       +1     
  Lines         570      590      +20     
  Branches      105      111       +6     
==========================================
+ Hits          567      587      +20     
  Misses          3        3