private let trueNumber = NSNumber(bool: true)
private let falseNumber = NSNumber(bool: false)
private let trueObjCType = String.fromCString(trueNumber.objCType)
private let falseObjCType = String.fromCString(falseNumber.objCType)

extension NSNumber {
    var isBool: Bool {
        get {
            let objCType = String.fromCString(self.objCType)
            if (self.compare(trueNumber) == NSComparisonResult.OrderedSame && objCType == trueObjCType)
                || (self.compare(falseNumber) == NSComparisonResult.OrderedSame && objCType == falseObjCType){
                return true
            } else {
                return false
            }
        }
    }
}

代碼來(lái)自于SwiftyJSON
可見(jiàn)每一個(gè)NSNumber（繼承自NSValue）都有一個(gè)objCType屬性，標(biāo)明其Objective-C數(shù)據(jù)類型。OC中可以用@encode編譯器命令。具有同樣效果。SwiftyJSON中寫得這么啰嗦一定是為了可讀性。

- (void)someMethod {
    char *intCharArray = @encode(int);
    char *boolCharArray = @encode(BOOL);
    if (strcmp(intCharArray, boolCharArray) == 0) {
        NSLog(@"兩個(gè)字符串相等");
    }
}