Mapped types and generics

The code explain herself, but it's basically you type a interface without say if it should be a string or number, but after used it should follow the first called type
// The video for this file: // export interface Cat { age: number; name: string; eat(): void; } type ReadonlyCat = { readonly [P in keyof Cat]: Cat[P]; } type GenericReadonly<T> = { readonly [P in keyof T]: T[P]; } type ReadonlyCat2 = GenericReadonly<Cat>; // Transformo em não obrigatório os campos type GenericPartial<T> = { [P in keyof T]?: T[P]; } type PartialCat = GenericPartial<Cat>; type ReadonlyPartialCat = GenericReadonly<PartialCat>; type GenericNullable<T> = { [P in keyof T]: T[P] | null; } type NullableCat = GenericNullable<Cat>; interface Proxy<T> { get(): T; set(value: T): void; } // Reutilizo uma interface, agora cada T irá ter um get set type Proxied<T> = { [P in keyof T]: Proxy<T[P]>; } type ProxiedCat = Proxied<Cat>; const cat: ProxiedCat = null; cat.age.get(); type A = Readonly<Cat>; type B = Partial<Cat>; type C = Pick<Cat, 'age' | 'eat'>;
The video I used as reference:
Video preview