I have these two interfaces
interface PersonRequirements{ user:string, password:string, id:number } export interface Requirement<R> { name: keyof R & string, save: () => any,/* I want this return type to be same as return type of founded key in R*/ }
and here is my use case elsewhere
const idRequirement:Requirement<PersonRequirements>={ name:"id", save:function ():number/* I want this return type to be same as id's return type(number) but in a generic type safe way*/{ // } }
I want to make save()
return type to be same as id’s return type but in a generic type safe way how can I do that ?
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Answer
You can declare another generic parameter that takes the property name in at compile time.
export interface Requirement<R, N extends keyof R & string> { name: N; // this will force the name property to be the same as being passed in save(): R[N]; }
Then using it like this
const idRequirement: Requirement<PersonRequirements, "id"> ={ name: "id", save: () => 0 }