Function “lacks return statement” but has typeguards for all the paths

Question

I have the following interfaces and types (all of which are open to change)

interface Base {
    type: string;
}

interface A extends Base {
    type: \"A\";         


        

Answer 1

If you're not going to throw any errors, and isC is your last rule check-point, couldn't you remove the condition (thus always returning the CThing at the end)?

function doAThingBasedOnTheRuleType(rule: Rule): Thing {
    if (isAnd(rule)) {
        return DoAndThing(rule);
    }
    if (isOr(rule)) {
        return DoOrThing(rule);
    }
    if (isA(rule.base)) {
        return DoAThing(rule);
    }
    if (isB(rule.base)) {
        return DoBThing(rule);
    }

    return DoCThing(rule);
}