Typescript条件类型和对象属性

T extends U ? X : Y

type User = {
    name: string;
    age: number;
    isAdmin: boolean;
};

type UserRole<T> = T extends { isAdmin: true } ? 'Admin' : 'User';

type AdminUser = UserRole<{ isAdmin: true }>; // 'Admin'
type RegularUser = UserRole<{ isAdmin: false }>; // 'User'

type UserWithOptionalEmail = {
    name: string;
    email?: string;
};

type HasEmail<T> = T extends { email: infer E } ? E : 'No Email';

type EmailType = HasEmail<UserWithOptionalEmail>; // string | undefined
type NoEmailType = HasEmail<{ name: string }>; // 'No Email'

type Config<T> = {
    [K in keyof T]: T[K] extends string ? string : number;
};

type OriginalConfig = {
    host: string;
    port: number;
    timeout: string;
};

type TransformedConfig = Config<OriginalConfig>;
// TransformedConfig 的类型为：
// {
//     host: string;
//     port: number;
//     timeout: string;
// }

type User = {
    name: string;
    age: number;
    isAdmin: boolean;
};

type ReadonlyUser<T> = {
    readonly [K in keyof T]: T[K];
};

type ReadonlyUserType = ReadonlyUser<User>;
// ReadonlyUserType 的类型为：
// {
//     readonly name: string;
//     readonly age: number;
//     readonly isAdmin: boolean;
// }