Remove Flag Argument

練習用的 REPL

function bookConcert(aCustomer, isPremium) {
    if (isPremium) {
        // logic for premium booking
    } else {
        // logic for regular booking
    }
}

// possible usage

bookConcert(aCustomer, true);
bookConcert(aCustomer, CustomerType.PREMIUM);
bookConcert(aCustomer, "premium");

// how about this ?

premiumBookConcert(aCustomer);

先用 Decompose Conditional 把 if-else 區塊抽取出來。

function deliveryDate(anOrder, isRush) {
    if (isRush) {
        let deliveryTime;
        if (["MA", "CT"].includes(anOrder.deliveryState)) deliveryTime = 1;
        else if (["NY", "NH"].includes(anOrder.deliveryState)) deliveryTime = 2;
        else deliveryTime = 3;
        return anOrder.placedOn.plusDays(1 + deliveryTime);
    } else {
        let deliveryTime;
        if (["MA", "CT", "NY"].includes(anOrder.deliveryState)) deliveryTime = 2;
        else if (["ME", "NH"].includes(anOrder.deliveryState)) deliveryTime = 3;
        else deliveryTime = 4;
        return anOrder.placedOn.plusDays(2 + deliveryTime);
    }
}

function deliveryDate(anOrder, isRush) {
    if (isRush) return rushDeliveryDate(anOrder);    // 把 flag 換成直接呼叫 function
    else        return regularDeliveryDate(anOrder); // 把 flag 換成直接呼叫 function
}


// 先做 decompose conditional，把 branch 分支拆出去

function rushDeliveryDate(anOrder) {
    let deliveryTime;
    if (["MA", "CT"].includes(anOrder.deliveryState)) deliveryTime = 1;
    else if (["NY", "NH"].includes(anOrder.deliveryState)) deliveryTime = 2;
    else deliveryTime = 3;
    return anOrder.placedOn.plusDays(1 + deliveryTime);
}

function regularDeliveryDate(anOrder) {
    let deliveryTime;
    if (["MA", "CT", "NY"].includes(anOrder.deliveryState)) deliveryTime = 2;
    else if (["ME", "NH"].includes(anOrder.deliveryState)) deliveryTime = 3;
    else deliveryTime = 4;
    return anOrder.placedOn.plusDays(2 + deliveryTime);
}

然後就可以更改呼叫端的程式。

// 原本的 caller
aShipment.deliveryDate = deliveryDate(anOrder, true);
// 可以改成以下形式
aShipment.deliveryDate = rushDeliveryDate(anOrder);

// 保留這個 function 是要讓還沒改好的 caller 不要壞掉
function deliveryDate(anOrder, isRush) {
    if (isRush) return rushDeliveryDate(anOrder);
    else        return regularDeliveryDate(anOrder);
}

function rushDeliveryDate(anOrder) {
    let deliveryTime;
    if (["MA", "CT"].includes(anOrder.deliveryState)) deliveryTime = 1;
    else if (["NY", "NH"].includes(anOrder.deliveryState)) deliveryTime = 2;
    else deliveryTime = 3;
    return anOrder.placedOn.plusDays(1 + deliveryTime);
}

function regularDeliveryDate(anOrder) {
    let deliveryTime;
    if (["MA", "CT", "NY"].includes(anOrder.deliveryState)) deliveryTime = 2;
    else if (["ME", "NH"].includes(anOrder.deliveryState)) deliveryTime = 3;
    else deliveryTime = 4;
    return anOrder.placedOn.plusDays(2 + deliveryTime);
}

有時候，實在太複雜了，只好先包起來，下次再行梳理。

function deliveryDate(anOrder, isRush) {
    let result;
    let deliveryTime;
    if (anOrder.deliveryState === "MA" || anOrder.deliveryState === "CT")
        deliveryTime = isRush ? 1 : 2;
    else if (anOrder.deliveryState === "NY" || anOrder.deliveryState === "NH") {
        deliveryTime = 2;
        if (anOrder.deliveryState === "NH" && !isRush)
            deliveryTime = 3;
    } else if (isRush)
        deliveryTime = 3;
    else if (anOrder.deliveryState === "ME")
        deliveryTime = 3;
    else
        deliveryTime = 4;
    result = anOrder.placedOn.plusDays(2 + deliveryTime);
    if (isRush) result = result.minusDays(1);
    return result;
}

// 只好包起來，眼不見為淨
// 或是下次需要調整 logic 時再行梳理
function rushDeliveryDate   (anOrder) {return deliveryDate(anOrder, true);}
function regularDeliveryDate(anOrder) {return deliveryDate(anOrder, false);}