php - 为什么 switch(true) 的 NPath 复杂度比 if() elseif() 小？

Question

我有这个函数负责将文件名和 mime 类型转换为更“人性化”的东西(例如 file.png、image/png 到 [Image, PNG])。我发现有趣的是，if() elseif() 语句组的 NPath 复杂度高于 switch(true) 语句。

使用以下代码，PHP Mess Detector 输出 4410 的 NPath:

public function humanKind()
{
    $typeRA = explode("/", strtolower($this->type));
    $fileRA = explode(".", $this->name);
    $fileType = strtoupper($fileRA[count($fileRA) - 1]);

    switch($typeRA[0]) {
        case "image":
            $humanType = "Image";
            break;
        case "video":
            $humanType = "Video";
            break;
        case "audio":
            $humanType = "Sound";
            break;
        case "font":
            $humanType = "Font";
            break;
        default:
            $humanType = "File";
    }

    switch ($this->type) {
        case "application/msword":
        case "application/pdf":
        case "applicaiton/wordperfect":
        case "text/plain":
        case "text/rtf":
        case "image/vnd.photoshop":
        case "image/psd":
        case "image/vnd.adobe.photoshop":
        case "image/x-photoshop":
        case "application/xml":
        case "application/x-mspublisher":
        case "text/html":
        case "application/xhtml+xml":
        case "text/richtext":
        case "application/rtf":
        case "application/x-iwork-pages-sffpages":
        case "application/vnd.apple.pages":
            $humanType = "Document";
            break;
        case "application/vnd.ms-excel":
        case "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet":
        case "application/x-iwork-numbers-sffnumbers":
        case "application/vnd.apple.numbers":
            $humanType = "Spreadsheet";
            break;
        case "application/vnd.ms-powerpoint":
        case "application/vnd.openxmlformats-officedocument.presentationml.presentation":
        case "application/vnd.openxmlformats-officedocument.presentationml.slideshow":
        case "application/x-iwork-keynote-sffkey":
        case "application/vnd.apple.keynote":
            $humanType = "Slideshow";
            break;
        case "application/zip":
        case "application/x-zip-compressed":
        case "application/x-compressed":
        case "application/x-compress":
        case "application/x-rar-compressed":
        case "applicaiton/x-7z-compressed":
        case "application/x-ace-compressed":
            $humanType = "Archive";
            break;
        case "text/x-vcard":
        case "text/x-ms-contact":
            $humanType = "Contact";
            break;
        case "text/x-php":
        case "application/x-dosexec":
        case "application/x-xpinstall":
        case "application/x-opera-extension":
        case "application/x-chrome-extension":
        case "application/x-perl":
        case "application/x-shockwave-flash":
        case "application/java-archive":
            $humanType = "Program";
            break;
        case "application/vnd.ms-fontobject":
        case "application/font-woff":
        case "application/x-font-truetype":
        case "application/x-font-opentype":
        case "application/x-font-ttf":
        case "application/font-sfnt":
            $humanType = "Font";
            break;
    }

    // Special Cases
    if ($humanType == "Archive" && $fileType == "APK") { // Android App
        $humanType = "App";
    } elseif ($humanType == "Archive" && $fileType == "XPS") {
        $humanType = "Document";
    } elseif ($this->type == "application/xml" && $fileType == "CONTACT") {
        $humanType = "Contact";
    } elseif ($this->type == "application/octet-stream" && $fileType == "JNT") {
        $humanType = "Document";
    }

    if (strlen($fileType) > 4) {
        $fileType = "";
    }

    return array($humanType, $fileType);

如果我们将特殊情况 if elseif 替换为以下内容:

    // Special Cases
    switch(true) {
        case ($humanType == "Archive" && $fileType == "APK"): // Android App
            $humanType = "App";
            break;
        case ($humanType == "Archive" && $fileType == "XPS"):
            $humanType = "Document";
            break;
        case ($this->type == "application/xml" && $fileType == "CONTACT"):
            $humanType = "Contact";
            break;
        case ($this->type == "application/octet-stream" && $fileType == "JNT"):
            $humanType = "Document";
            break;
    }

PHP Mess Detector 报告 1960 年的 NPath 复杂度。

这是为什么？是什么让 switch(true) 比我看来的几乎相同的控制结构更简单？

Answer 1

由于 NPath 复杂性衡量完成所需的单元测试数量 coverage of your code您的 2 个“特例”实现应该没有区别。

但是在计算上有些差异。让我们逐步完成 2 个“特例”实现并手动计算 NPath 复杂度:

NPath 复杂度与 if .. elseif ..

if ($humanType == "Archive" && $fileType == "APK") { // Android App
    $humanType = "App";
} 
elseif ($humanType == "Archive" && $fileType == "XPS") {
    $humanType = "Document";
} 
elseif ($this->type == "application/xml" && $fileType == "CONTACT") {
    $humanType = "Contact";
} 
elseif ($this->type == "application/octet-stream" && $fileType == "JNT") {
    $humanType = "Document";
}

此语句的 NPath 复杂度为 9:if .. else 为 1 分，每个 if(expr) 为 1 分，并且每个 && 运算符得 1 分。 (1 + 4 + 4 = 9)

NPath 复杂度与 switch(true)

switch(true) {
    case ($humanType == "Archive" && $fileType == "APK"): // Android App
        $humanType = "App";
        break;
    case ($humanType == "Archive" && $fileType == "XPS"):
        $humanType = "Document";
        break;
    case ($this->type == "application/xml" && $fileType == "CONTACT"):
        $humanType = "Contact";
        break;
    case ($this->type == "application/octet-stream" && $fileType == "JNT"):
        $humanType = "Document";
        break;
}

并且此语句导致 NPath 复杂度仅为 4:switch(true) 为 0 分，因为它不包含 && 或 || 运算符，每个 case 标签得 1 分。 (0 + 4 = 4)

humanKind 函数的 NPath 复杂度

为每个语句计算 NPath 值，然后将这些值相乘。没有“特殊情况”语句的函数的 NPath 复杂度为 490。乘以 9 的 if .. else if .. 语句的 NPath 值，您得到 4410 的 NPath 复杂度。并相乘使用 4 的 switch(true) 语句的 NPath 值，您得到的复杂度仅为 1960。这就是全部!

现在我们知道:NPath Complexity 不衡量 switch 语句中 case 标签的表达式复杂性!