我一直在尝试在类中使用常量和变量，这些常量和变量在类级别上按名称引用同一类中的其他常量和变量。AFAIK，从Xcode 6 beta
4开始，Swift仍然没有类变量支持。我想知道的是，当我尝试引用其他常量（let）或变量（var）时看到的错误是否仅仅是由于缺少类变量支持？

您可以在方法内或类外部引用常量和变量，只是似乎无法在类级别按名称引用。下列类别显示了几种变体，以及将在Xcode 6 beta 4中显示的错误。

可以在游乐场或常规.swift文件中进行测试。

class Simple {

    let someConstant = 0.50

    var someVariable = 1

    // uncomment let and var lines to see the errors

    // error: 'Simple.Type' does not have a member named 'someConstant'
    // let referringConstant = someConstant
    // error: Use of unresolved identifier 'self'
    // let referringConstant = self.someConstant

    // error: 'Simple.Type' does not have a member named 'someVariable'
    // var referringVar = someVariable
    // error: Use of unresolved identifier 'self'
    // var referringVar = self.someVariable

    // can't do class constants or variables yet either
    // let referringConstant = Simple.someConstant
    // var referringVar = Simple.someVariable

    func simpleMethod() {
        // both of these forms are valid as long as it is unambiguous
        let referToConstant = someConstant
        let referToVariable = someVariable

        var anotherConstant = self.someConstant
        var anotherVariable = self.someVariable
    }
}

作为参考，导致Swift中出现此问题的原始Objective-C代码来自CS193P SuperCard应用，其中C

define用于常量，然后使用该常量设置变量。

@interface PlayingCardView()
@property (nonatomic) CGFloat faceCardScaleFactor;
@end

@implementation PlayingCardView

#pragma mark - Properties

@synthesize faceCardScaleFactor = _faceCardScaleFactor;

#define DEFAULT_FACE_CARD_SCALE_FACTOR 0.90

- (CGFloat)faceCardScaleFactor
{
    if (!_faceCardScaleFactor) _faceCardScaleFactor = DEFAULT_FACE_CARD_SCALE_FACTOR;
        return _faceCardScaleFactor;
}

- (void)setFaceCardScaleFactor:(CGFloat)faceCardScaleFactor
{
    _faceCardScaleFactor = faceCardScaleFactor;
    [self setNeedsDisplay];
}