todays-mitsui/InferSchema.ts

## InferSchema.ts
// 文字列リテラル型を対応するプリミティブ型に変換する
type Lift<T> = T extends readonly [ string, ...string[] ] ? LiftTuple<T>
	: T extends 'null' ? null
	: T extends 'boolean' ? boolean
	: T extends 'object' ? { [ key: string ]: any }
	: T extends 'array' ? any[]
	: T extends 'string' ? string
	: T extends 'number' | 'integer' ? number
	: any;

// 上記の変換のタプル版、空タプルは受け付けない
type LiftTuple<T> = T extends readonly [ infer Head, ...infer Tail ]
	? Tail extends [ string, ...string[] ]
		? Lift<Head> | LiftTuple<Tail>
		: Lift<Head>
	: never;


// ↓↓↓ 使ってみる

type T1 = Lift<'string'>;
//   ^ = string

type T2 = Lift<'integer'>;
//   ^ = number

type T3 = Lift<readonly [ 'string', 'integer', 'null' ]>;
//   ^ string | number | null

// ========================================================================== //

// schema から型定義を作る
type InferSchema<T extends { [key: string]: { type: string | readonly string[] } }>
  = { [K in keyof T]: Lift<T[K]['type']> }


// ↓↓↓ 使ってみる

const attributes = {
  foo: { type: 'string', default: '' },
  bar: { type: 'integer' },
  buz: { type: 'boolean' },
  qux: { type: [ 'string', 'null' ] }
} as const;

type Attributes = InferSchema<typeof attributes>;
//   ^ = {
//      readonly foo: string;
//      readonly bar: number;
//      readonly buz: boolean;
//      readonly qux: string | null;
//    }
	// 文字列リテラル型を対応するプリミティブ型に変換する
	type Lift<T> = T extends readonly [ string, ...string[] ] ? LiftTuple<T>
	: T extends 'null' ? null
	: T extends 'boolean' ? boolean
	: T extends 'object' ? { [ key: string ]: any }
	: T extends 'array' ? any[]
	: T extends 'string' ? string
	: T extends 'number' \| 'integer' ? number
	: any;

	// 上記の変換のタプル版、空タプルは受け付けない
	type LiftTuple<T> = T extends readonly [ infer Head, ...infer Tail ]
	? Tail extends [ string, ...string[] ]
	? Lift<Head> \| LiftTuple<Tail>
	: Lift<Head>
	: never;


	// ↓↓↓ 使ってみる

	type T1 = Lift<'string'>;
	// ^ = string

	type T2 = Lift<'integer'>;
	// ^ = number

	type T3 = Lift<readonly [ 'string', 'integer', 'null' ]>;
	// ^ string \| number \| null

	// ========================================================================== //

	// schema から型定義を作る
	type InferSchema<T extends { [key: string]: { type: string \| readonly string[] } }>
	= { [K in keyof T]: Lift<T[K]['type']> }


	// ↓↓↓ 使ってみる

	const attributes = {
	foo: { type: 'string', default: '' },
	bar: { type: 'integer' },
	buz: { type: 'boolean' },
	qux: { type: [ 'string', 'null' ] }
	} as const;

	type Attributes = InferSchema<typeof attributes>;
	// ^ = {
	// readonly foo: string;
	// readonly bar: number;
	// readonly buz: boolean;
	// readonly qux: string \| null;
	// }