xcode – ‘Class.Type’没有一个名为’variable’的成员,只是缺少类变量支持？

我一直在尝试在一个类中使用常量和变量,该类通过名称引用到类级别的同一个类中的其他常量和变量. AFAIK,截至 Xcode 6 beta 4,Swift仍然没有类变量支持.我想知道的是,当试图引用其他常量(let)或变量(var)时,我看到的错误是否仅仅是由于缺少类变量支持？

您可以参考一个方法或类之外的常量和变量,但您似乎无法在类级别中引用名称.以下课程显示了您将在Xcode 6 beta 4中显示的错误以及几个变体.

这可以在操场或常规.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,在Swift中导致此问题的原始Objective-C代码来自cs193p SuperCard应用程序,其中使用c#define用于常量,然后该常量用于设置变量.

@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];
}

struct Simple {
    static let someConstant = 0.50
    static var someVariable = 1

    let referringConstant = someConstant
    var referringVar = someVariable

    let explicitTypeProperty = Simple.someConstant
}