feat: add some comments for types

Author: kakasoo

src/types/DeepDateToString.ts

@@ -1,3 +1,10 @@
+/**
+ * A utility type that recursively converts all `Date` types within a nested object or array to `string`.
+ *
+ * - If `T` is an array of objects, the type processes each element recursively.
+ * - If `T` is a `Date`, it is converted to `string`.
+ * - If `T` is an object, each key is checked recursively for `Date` types or nested objects.
+ */
 export type DeepDateToString<T> =
   T extends Array<infer I extends object>
     ? Array<DeepDateToString<I>>

src/types/DeepStrictObjectKeys.ts

@@ -32,10 +32,11 @@ type __DeepStrictObjectKeys<
   : never;
 
 /**
- * @title 중첩된 객체 혹은 배열의 모든 키를 표기하는 타입.
+ * @title Type for Listing All Keys of Nested Objects or Arrays.
  *
- * 중첩된 객체의 모든 키를 뽑는 타입으로, 만약 중첩된 객체가 있을 경우 점 기호를 기준으로 객체를 표현한다.
- * 배열인 경우에는 `[*]` 기호를 이용하여 표기한다.
+ * A type that extracts all keys of a nested object. If the object contains nested properties,
+ * the keys are represented using dot notation. For arrays, the keys are represented using
+ * the `[*]` symbol.
  *
  * ```ts
  * type Example1 = DeepStrictObjectKeys<{ a: { b: 1; c: 2 } }>; // "a" | "a.b" | "a.c"

src/types/DeepStrictOmit.ts

@@ -37,13 +37,20 @@ type _DeepStrictOmit<T extends object, K extends DeepStrictObjectKeys<T>> =
     : ____DeepStrictOmit<T, K>;
 
 /**
- * @title 인터페이스에서 특정 키를 제거하는 타입.
- * {@link DeepStrictObjectKeys} 을 이용해서 제거할 키를 고를 수 있다.
+ * @title Type for Removing Specific Keys from an Interface.
  *
+ * The `DeepStrictOmit<T, K>` type creates a new type by excluding properties
+ * corresponding to the key `K` from the object `T`, while preserving the nested structure.
+ * It enables precise omission of keys even in deeply nested objects or arrays.
+ *
+ * {@link DeepStrictObjectKeys} can be used to determine valid keys for omission,
+ * including nested keys represented with dot notation (`.`) and array indices represented with `[*]`.
+ *
+ * Example Usage:
  * ```ts
- * type Example1 = DeepStrictOmit<{ a: { b: 1; c: 2 } }, "a.b">;
- * type Example2 = DeepStrictOmit<{ a: { b: 1; c: { d: number }[] } }, "a.c[*].d">;
- * type Example3 = DeepStrictOmit<{ a: 1 }[], "[*].a">;
+ * type Example1 = DeepStrictOmit<{ a: { b: 1; c: 2 } }, "a.b">; // { a: { c: 2 } }
+ * type Example2 = DeepStrictOmit<{ a: { b: 1; c: { d: number }[] } }, "a.c[*].d">; // { a: { b: 1; c: {}[] } }
+ * type Example3 = DeepStrictOmit<{ a: 1 }[], "[*].a">; // {}[]
  * ```
  */
 export type DeepStrictOmit<T extends object, K extends DeepStrictObjectKeys<DeepStrictUnbrand<T>>> = _DeepStrictOmit<

src/types/DeepStrictPick.ts

@@ -5,13 +5,20 @@ import type { RemoveAfterDot } from './RemoveAfterDot';
 import type { RemoveLastProperty } from './RemoveLastProperty';
 
 /**
- * @title 인터페이스에서 특정 키만을 뽑는 타입.
- * {@link DeepStrictObjectKeys} 을 이용해서 뽑을 키를 고를 수 있다.
+ * @title Type for Selecting Specific Keys from an Interface.
  *
+ * The `DeepStrictPick<T, K>` type creates a new type by selecting only the properties
+ * corresponding to the key `K` from the object `T`, while preserving the nested structure.
+ * This type allows safely selecting specific keys, even from deeply nested objects or arrays.
+ *
+ * {@link DeepStrictObjectKeys} can be used to determine valid keys for selection,
+ * including nested keys represented with dot notation (`.`) and array indices represented with `[*]`.
+ *
+ * Example Usage:
  * ```ts
- * type Example1 = DeepStrictPick<{ a: { b: 1; c: 2 } }, "a.b">;
- * type Example2 = DeepStrictPick<{ a: { b: 1; c: { d: number }[] } }, "a.c[*].d">;
- * type Example3 = DeepStrictPick<{ a: 1 }[], "[*].a">;
+ * type Example1 = DeepStrictPick<{ a: { b: 1; c: 2 } }, "a.b">; // { a: { b: 1 } }
+ * type Example2 = DeepStrictPick<{ a: { b: 1; c: { d: number }[] } }, "a.c[*].d">; // { a: { c: { d: number }[] } }
+ * type Example3 = DeepStrictPick<{ a: 1 }[], "[*].a">; // { a: 1 }[]
  * ```
  */
 export type DeepStrictPick<T extends object, K extends DeepStrictObjectKeys<T>> = DeepStrictOmit<

src/types/DeepStrictUnbrand.ts

@@ -13,6 +13,30 @@ type Unbrand<T extends Primitive & Record<any, any>> = T extends string & Record
             ? Extract<undefined, Omit<T, any>>
             : T;
 
+/**
+ * @title Type for Recursively Removing Branding Types.
+ *
+ * The `DeepStrictUnbrand<T>` type recursively processes the type `T` to remove any branding
+ * that may have been added to primitive types or object properties. Branding often occurs when
+ * extending or augmenting primitive types for type safety, and this type "unbrands" them, restoring
+ * the original primitive type (e.g., `string`, `number`, `boolean`, etc.).
+ *
+ * The helper type `Unbrand<T>` is used to handle primitive types and their respective branding,
+ * by stripping off any additional properties that may have been added to them.
+ *
+ * The recursion goes through:
+ * - Arrays: It recursively processes elements of the array, maintaining deep unbranding.
+ * - Objects: It recursively processes each key in the object, unbranding any branded properties.
+ * - Primitives: It removes branding from primitive types (`string`, `number`, `boolean`, `symbol`, `null`, `undefined`).
+ * - Dates: The `Date` type is preserved as it is.
+ *
+ * Example Usage:
+ * ```ts
+ * type Example1 = DeepStrictUnbrand<{ a: string & { __brand: 'unique' } }>; // { a: string }
+ * type Example2 = DeepStrictUnbrand<{ a: { b: number & { __brand: 'id' } } }>; // { a: { b: number } }
+ * type Example3 = DeepStrictUnbrand<Array<string & { __brand: 'email' }>>; // Array<string>
+ * ```
+ */
 export type DeepStrictUnbrand<T> =
   T extends Array<Date>
     ? Array<Date>

src/types/ElementOf.ts

@@ -1,4 +1,4 @@
 /**
- * @title 배열의 요소 타입을 추론하는 타입.
+ * @title Type for Inferring the Element Type of an Array.
  */
 export type ElementOf<T extends Array<any>> = T extends Array<infer Element> ? Element : never;

src/types/Equal.ts

@@ -1,9 +1,13 @@
 /**
- * 구현 방법
+ * Implementation method
  */
 type Expression<X> = <T>() => T extends X ? 1 : 2;
 
 /**
- * @title 두 타입이 동일한 타입인지 확인하기 위한 타입
+ * @title Type for Checking if Two Types are Equal.
+ *
+ * The `Equal<X, Y>` type uses conditional types and a helper type `Expression<X>`
+ * to determine if two types `X` and `Y` are the same. It returns `true` if they are
+ * equal, and `false` otherwise.
  */
 export type Equal<X, Y> = Expression<X> extends Expression<Y> ? true : false;

src/types/GetMember.ts

@@ -1,15 +1,29 @@
 /**
- * @title 어떤 키로부터 멤버만을 조회하는 타입.
+ * @title Type for Retrieving Members from a Specific Key.
  *
+ * The `GetMember<T, O>` type extracts the part of the key `T` after the given prefix key `O`.
+ * If `T` starts with `O`, it returns the remaining portion of the key after `O`.
+ *
+ * Example Usage:
  * ```ts
- * type b = GetMember<"a.b", "a">;
- * type b_c = GetMember<"a.b.c", "a">;
+ * type b = GetMember<"a.b", "a">; // "b"
+ * type b_c = GetMember<"a.b.c", "a">; // "b.c"
  * ```
  */
 export type GetMember<T extends string, O extends string> = T extends `${O}.${infer Rest}` ? Rest : never;
 
 /**
- * @title 어떤 키로부터 요소 멤버의 키를 조회하는 타입.
+ * @title Type for Retrieving the Key of an Element Member from a Specific Key.
+ *
+ * The `GetElementMember<T, First>` type handles both regular keys and array element keys.
+ * If the key `T` represents an array element (denoted by `[*]`), it returns the key after the array element.
+ * Otherwise, it falls back to using `GetMember<T, First>` to retrieve the remaining portion of the key.
+ *
+ * Example Usage:
+ * ```ts
+ * type ElementKey = GetElementMember<"a[*].b", "a">; // "b"
+ * type NestedKey = GetElementMember<"a.b.c", "a">; // "b.c"
+ * ```
  */
 export type GetElementMember<T extends string, First extends string> = T extends `${First}[*].${infer Rest}`
   ? Rest

src/types/GetStrictObjectLastKeys.ts

@@ -30,6 +30,21 @@ type __DeepStrictObjectKeys<
             : never
   : never;
 
+/**
+ * @title Type for Extracting the Last Level Keys from Nested Objects, Including Array Elements.
+ *
+ * The `DeepStrictObjectLastKeys<T, Joiner, P>` type extracts the keys from the last level of a nested object `T`,
+ * with support for arrays. It returns keys with array indices (`[*]`) and object keys using a custom separator defined
+ * by the `Joiner` object.
+ * - For arrays, it appends array indices (`[*]`) followed by the key of the element.
+ * - For objects, it recursively traverses the nested structure and appends the last level keys.
+ *
+ * Example Usage:
+ * ```ts
+ * type Example1 = DeepStrictObjectLastKeys<{ a: { b: { c: number[] } } }>; // "a.b.c"
+ * type Example2 = DeepStrictObjectLastKeys<{ a: { b: number[]; c: { d: string }[] } }>; // "a.b" | "a.c" | "a.c[*].d"
+ * ```
+ */
 export type DeepStrictObjectLastKeys<
   T extends object,
   Joiner extends { array: string; object: string } = {

src/types/GetType.ts

@@ -16,12 +16,22 @@ type ToObject<T> = Allow<T, object>;
 
 /**
  * @title The type that pulls out the type of a particular key on an interface.
- * @template {T}
- * @template {K}
  *
+ * This type extracts the type of a specific key from a nested object,
+ * supporting arrays and deeply nested keys. It uses `DeepStrictObjectKeys`
+ * to handle the extraction of keys and correctly resolves the type for the given key.
+ *
+ * - If the key points to a primitive value, the type is returned directly.
+ * - If the key points to an array, the type of the array elements is resolved.
+ * - It supports nested keys using `.` notation to handle deep objects and arrays.
+ *
+ * @template T The interface type.
+ * @template K The key string, which can represent a nested key path.
+ *
+ * Example usage:
  * ```ts
  * type Example1 = GetType<{ a: { b: { c: number } } }, "a.b">; // { c: number }
- * type Example = GetType<{ a: { b: { c: number } } }, "a.b.c">; // number
+ * type Example2 = GetType<{ a: { b: { c: number } } }, "a.b.c">; // number
  * ```
  */
 export type GetType<T extends object, K extends DeepStrictObjectKeys<T>> =