How to use typegard for generics in TypeScript

Question

I defined following function.

const createAction = <I,O>(input: I, conditionFn: (_: I) => boolean, converter: (_: I) => O, restoreFn: (_: O) => any) => {
    if(conditionFn(input)){
        const converted = converter(input);
        return restoreFn(converted);
    }
    return undefined;
};

I want to use this function as follows.

const conditionAge = (age: number | undefined): age is number => typeof age === 'number';

const convertAge = (age: number) => age + '';

const setAge = (age: number) => {
    return {
        type: 'SET_AGE',
        payload: age
    }
};

// mock
const createAge = (value: number, isEmpty: boolean): number | undefined => isEmpty ? undefined : value;

const result = createAction(createAge(33), conditionAge, convertAge, setAge);
// Argument of type 'number | undefined' is not assignable to parameter of type 'number'.

But compile error occurred. I think generics I is not match. Is there any idea for this issue ??

Answer 1

等待大神解答