TypeScript Type Assertion Confusion with Mapped Types and Nested Objects
I recently switched to I'm working with an scenario with TypeScript where I'm trying to use type assertions with mapped types and nested objects... I have a structure where I'm defining a base type `User`, and then creating a mapped type for user roles. However, I'm running into type assertion problems when trying to access nested properties. Here's a simplified version of my code: ```typescript interface User { id: number; name: string; roles: string[]; } type UserRoles<T> = { [K in keyof T]: T[K] extends string[] ? 'Admin' | 'User' : T[K]; }; const users: User[] = [ { id: 1, name: 'Alice', roles: ['Admin'] }, { id: 2, name: 'Bob', roles: ['User'] } ]; const userRoles: UserRoles<User>[] = users.map(user => { return { ...user, roles: user.roles as UserRoles<User>['roles'] // Type assertion here }; }); ``` However, when I try to compile this, I get the following behavior: ``` Type 'string[]' is not assignable to type 'Admin | User'. ``` I thought that the type assertion on `roles` would help, but it seems like TypeScript isn't allowing the assignment due to the mapped type constraints. I've also tried to modify the `UserRoles` type to include a union type directly on `roles`, but that didn't work either. Is there a way to correctly assert the type here or an alternative approach I should consider? I'm using TypeScript version 4.5.2. Any insights would be greatly appreciated! Is there a better approach?