Discovering properties based on their types

Question

Discovering properties based on their types

My dilemma involves an interface set up as follows:

interface A {
   a: string;
}

interface B {
   b: string;
}

export interface C {
   rnd: A;
   rnd2: B;
}

I am seeking a function like update<T>(setting: T) which can identify the property of type T within an object that implements interface C, and then update the value of that property (if it already exists) with the passed setting.

Is there a method to accomplish this task? I attempted iterating and using typeof, but encountered the error message:

This condition will always return 'false' since types 'T' and 'string' has no overlap

typescript

Answer 1

Answer №1

To solve this issue, one approach is to provide the key name as a parameter. This way, the compiler can verify that the key name belongs to C and that the value parameter matches the type specified by the key in C:

interface A { a: string; }

interface B { b: string; }

export interface C { rnd: A; rnd2: B;}

let allSettings: C = {} as C
function update<K extends keyof C>(key: K, setting: C[K]) {
    allSettings[key]  = setting;
}

update("rnd", { a: "" }) // valid
update("rnd", { b: "" }) // invalid
update("rnd3", { b: "" }) // invalid

Answer 2

To solve this issue, one approach is to provide the key name as a parameter. This way, the compiler can verify that the key name belongs to C and that the value parameter matches the type specified by the key in C:

interface A { a: string; }

interface B { b: string; }

export interface C { rnd: A; rnd2: B;}

let allSettings: C = {} as C
function update<K extends keyof C>(key: K, setting: C[K]) {
    allSettings[key]  = setting;
}

update("rnd", { a: "" }) // valid
update("rnd", { b: "" }) // invalid
update("rnd3", { b: "" }) // invalid

Discovering properties based on their types

Answer №1

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