I have two string literals and created an interface based on those string literals as follows:

type context = 'a' | 'b';

type statusKey = 'aTest' | 'aFinal' | 'bTest' | 'cTest'

interface State {
    status: {
        [c in context]: {
            [key in statusKey]: {
                seen: number;
                total: number;
            }
        }
    }
}

Now, I want to restrict the inner object's keys such that: it should only allow keys that starts with key of its parent object.

So, as per my example, the valid status object should be:

    a: { 
        aTest: {
            seen: number;
            total: number;
        };
        aFinal: {
            seen: number;
            total: number;
        };
    };
    b: {
        bTest: {
            seen: number;
            total: number;
        };
    };

So, inshort a should not allow keys that does not start with a and b should not allow keys that does not start with b.

CodePudding user response：

The Extract utility type will help us to extract every string literal from statusKey which is assignable to the template literal type ${C}{string}.

interface State {
    status: {
        [C in context]: {
            [Key in Extract<statusKey, `${C}${string}`>]: {
                seen: number;
                total: number;
            }
        }
    }
}

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