c++ - 当两个功能非常相似时，如何避免复制和粘贴？

Question

我经常遇到结构和逻辑相同但有一些差异的方法，我找不到不重复自己的适当方法。

例如 :

void ChannelSelection::selectAlmostOkChannels(int currentInkId)
{
    bool selected = true;
    foreach (auto report, m_reports) {
        if (report.scoreByInk.find(currentInkId) != report.scoreByInk.end()) {
            auto tmpStatus = Assessment::getStatusFromScore(report.scoreByInk.value(currentInkId));
            if (tmpStatus == Assessment::Ok)
                selected = false;
            else if (tmpStatus == Assessment::NotOk)
                m_autoSelection[report.name].setSelected(currentInkId, false);
        }
    }
    m_currentSelection.insert(currentInkId, selected);
}

void ChannelSelection::selectNotOkChannels(int currentInkId)
{
    bool selected = true;
    foreach (auto report, m_reports) {
        if (report.scoreByInk.find(currentInkId) != report.scoreByInk.end()) {
            auto tmpStatus = Assessment::getStatusFromScore(report.scoreByInk.value(currentInkId));
            if (tmpStatus == Assessment::Ok || tmpStatus == Assessment::AlmostOk)
                selected = false;
        }
    }
    m_currentSelection.insert(currentInkId, selected);
}

如您所见，这两个函数非常相似(只有内部 if 不同)。我怎样才能很好地删除这段代码中的重复？

我想到的解决方案之一是使用仿函数，例如:

void ChannelSelection::selectChannels(int currentInkId, std::function<bool()> fn)
{
    bool selected = true;
    foreach (auto report, m_reports) {
        if (report.scoreByInk.find(currentInkId) != report.scoreByInk.end()) {
            auto tmpStatus = Assessment::getStatusFromScore(report.scoreByInk.value(currentInkId));
            selected = fn();
        }
    }
    m_currentSelection.insert(currentInkId, selected);
}

调用者负责实现仿函数。有没有没有这个问题的替代方案？

Answer 1

您不必将参数化 selectChannels上市。它可以是 selectAlmostOkChannels 的私有(private)实现细节和 selectNotOkChannels , 你的公共(public)函数。
selectChannels甚至可以实现为函数模板，使生成的代码相当于手写“复制粘贴”的版本，没有代码重复的维护负担

template<typename SelectFunction>
void ChannelSelection::selectChannels(int currentInkId, SelectFunction selectFn)
{
    bool selected = true;
    foreach (auto report, m_reports) {
        if (report.scoreByInk.find(currentInkId) != report.scoreByInk.end()) {
            auto tmpStatus = Assessment::getStatusFromScore(report.scoreByInk.value(currentInkId));
            selected = selectFn(tmpStatus);
            /* fill in */
        }
    }
    m_currentSelection.insert(currentInkId, selected);
}

void ChannelSelection::selectAlmostOkChannels(int currentInkId)
{
    selectChannels(currentInkId, [] (auto tmpStatus) -> bool {
        return /* fill in */;
    });
}

void ChannelSelection::selectNotOkChannels(int currentInkId)
{
    selectChannels(currentInkId, [] (auto tmpStatus) -> bool {
        return /* fill in */;
    });
}

您可能已经被告知模板需要在标题中，但这实际上并不是全部!模板定义需要在实例化的地方可见。由于您的模板仅用于成员函数的私有(private)实现，因此您的模板定义可以在实现两个成员函数的同一个文件中