subscript

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subscript 是 Swift 中特有的一个方法。该方法可以让我们更方便的实现的一些功能。例如数组中，array[index]，这样的实现其实都是通过 subscript 来实现。

那么，我们可以用 subscript 来干嘛呢？比如可以自定义 String 的 subscript，来达到更方便的切割字符串的功能。

String Extension

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extension String {
    
    /// 从开始位置截取到 index 位置
    ///
    /// - Parameter index: 所要截取到的位置
    /// - Returns: String
    func substring(to idx: Int) -> String {
        
        guard idx >= 0 else { return "" }
        
        guard idx < count else { return self }
        
        let endIndex = self.index(self.startIndex, offsetBy: idx)
        
        return String(self[...endIndex])
    }
    
    /// 从 index 位置开始截取
    ///
    /// - Parameter index: 所要开始截取的位置
    /// - Returns: String
    func substring(from idx: Int) -> String {
        
        guard idx >= 0 else { return self }
        
        guard idx < count else { return "" }
        
        let startIndex = self.index(self.startIndex, offsetBy: idx)
        
        return String(self[startIndex...])
        
    }
    
    /// eg: "swift"[r: 0..<3]     // "swi"
    ///
    /// - Parameter range: 开区间
    subscript(r range: CountableRange<Int>) -> String {
        
        guard range.lowerBound >= 0 else {
            return substring(to: range.upperBound)
        }
        
        guard range.upperBound < count else {
            return substring(from: range.lowerBound)
        }
        
        let startIndex = self.index(self.startIndex, offsetBy: range.lowerBound)
        let endIndex = self.index(self.startIndex, offsetBy: range.upperBound)
        
        return String(self[startIndex..<endIndex])
    }
    
    /// eg: "swift"[r: 0...3]     // "swif"
    ///
    /// - Parameter range: 闭区间
    subscript(r range: CountableClosedRange<Int>) -> String {
        
        guard range.lowerBound >= 0 else {
            return substring(to: range.upperBound)
        }
        
        guard range.upperBound < count else {
            return substring(from: range.lowerBound)
        }
        
        let startIndex = self.index(self.startIndex, offsetBy: range.lowerBound)
        let endIndex = self.index(self.startIndex, offsetBy: range.upperBound)
        
        return String(self[startIndex...endIndex])
        
    }
    
    /// eg: "swift"[r:1...]    // “wift”
    ///
    /// - Parameter range: PartialRangeFrom
    subscript(r range: PartialRangeFrom<Int>) -> String {
        guard range.lowerBound >= 0 else {
            return self
        }
        
        let startIndex = self.index(self.startIndex, offsetBy: range.lowerBound)
        return String(self[startIndex...])
    }
}

Array Extension

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extension Array {
    
    /// eg: [1,2][s: 4]        // nil
    ///
    /// - Parameter idx: index
    subscript(s idx: Int) -> Element? {
        
        guard 0..<count ~= idx else { return nil}
        
        return self[idx]
    }
    
}
extension Array where Element: Equatable {
    
    /// eg: [1,2][e: 1]        // 1
    ///
    /// - Parameter element: element
    subscript(e element: Element) -> Int? {
        
        return firstIndex(of: element)
        
    }
}

NSMutableAttributedString Extension

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extension NSMutableAttributedString {
    
    /// 检查是否越界
    ///
    /// - Parameter range: range
    private func check(_ range: inout NSRange) {
        if range.location + range.length > string.count {
            range = NSRange(location: range.location, length: string.count - range.location)
        }
    }
    
    /// all
    private var allRange : NSRange {
        return NSRange(location: 0, length: string.count)
    }
}
extension NSMutableAttributedString {
    /// eg: attributedStr[.font] = UIFont.boldSystemFont(ofSize: 20)
    subscript<T>(_ key: NSAttributedString.Key) -> T? {
        get {
            var range = allRange
            return attribute(key, at: 0, effectiveRange: &range) as? T
        }
        
        set {
            if let value = newValue {
                let range = allRange
                addAttribute(key, value: value, range: range)
            }
        }
    }
}
// MARK: NSMutableAttributedString + Range
extension NSMutableAttributedString {
    
    /// eg: attributedStr[.font, 0..<3] = UIFont.boldSystemFont(ofSize: 20)
    subscript<T>(_ key: NSAttributedString.Key, r: Range<Int>) -> T? {
        get {
            var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound)
            check(&range)
            return attribute(key, at: 0, effectiveRange: &range) as? T
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound)
                check(&range)
                addAttribute(key, value: value, range: range)
            }
        }
    }
    
    subscript<T>(_ key: NSAttributedString.Key, r: Range<String.Index>) -> T? {
        get {
            let lowerBound = r.lowerBound.encodedOffset
            let upperBound = r.upperBound.encodedOffset
            var range = NSRange(location: lowerBound, length: upperBound - lowerBound)
            check(&range)
            return attribute(key, at: 0, effectiveRange: &range) as? T
        }
        
        set {
            if let value = newValue {
                let lowerBound = r.lowerBound.encodedOffset
                let upperBound = r.upperBound.encodedOffset
                var range = NSRange(location: lowerBound, length: upperBound - lowerBound)
                check(&range)
                addAttribute(key, value: value, range: range)
            }
        }
    }
    
    /// eg: attributedStr[0..<3] = [.font: UIFont.boldSystemFont(ofSize: 20)]
    subscript<T>(_ r: Range<Int>) -> [NSAttributedString.Key: T]? {
        
        get {
            var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound)
            check(&range)
            var dict : [NSAttributedString.Key: T] = [:]
            enumerateAttributes(in: range, options: .longestEffectiveRangeNotRequired) { (atts, range, pointer) in
                dict = atts as! [NSAttributedString.Key : T]
            }
            
            return dict
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound)
                check(&range)
                value.forEach {
                    addAttribute($0, value: $1, range: range)
                }
            }
        }
        
    }
}
// MARK: NSMutableAttributedString + ClosedRange
extension NSMutableAttributedString {
    
    /// eg: attributedStr[.font, 0...3] = UIFont.boldSystemFont(ofSize: 20)
    subscript<T>(_ key: NSAttributedString.Key, r: ClosedRange<Int>) -> T? {
        get {
            var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound + 1)
            check(&range)
            return attribute(key, at: 0, effectiveRange: &range) as? T
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound + 1)
                check(&range)
                addAttribute(key, value: value, range: range)
            }
        }
    }
    
    /// eg: attributedStr[0...3] = [.font: UIFont.boldSystemFont(ofSize: 20)]
    subscript<T>(_ r: ClosedRange<Int>) -> [NSAttributedString.Key: T]? {
        
        get {
            var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound + 1)
            check(&range)
            var dict : [NSAttributedString.Key: T] = [:]
            enumerateAttributes(in: range, options: .longestEffectiveRangeNotRequired) { (atts, range, pointer) in
                dict = atts as! [NSAttributedString.Key : T]
            }
            
            return dict
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: r.upperBound - r.lowerBound + 1)
                check(&range)
                value.forEach {
                    addAttribute($0, value: $1, range: range)
                }
            }
        }
        
    }
    
}
// MARK: NSMutableAttributedString + PartialRangeFrom
extension NSMutableAttributedString {
    
    /// eg: attributedStr[.font, 3...] = UIFont.boldSystemFont(ofSize: 20)
    subscript<T>(_ key: NSAttributedString.Key, r: PartialRangeFrom<Int>) -> T? {
        get {
            var range = NSRange(location: r.lowerBound, length: string.count - r.lowerBound)
            check(&range)
            return attribute(key, at: 0, effectiveRange: &range) as? T
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: string.count - r.lowerBound)
                check(&range)
                addAttribute(key, value: value, range: range)
            }
        }
    }
    
    /// eg: attributedStr[3...] = [.font: UIFont.boldSystemFont(ofSize: 20)]
    subscript<T>(_ r: PartialRangeFrom<Int>) -> [NSAttributedString.Key: T]? {
        
        get {
            var range = NSRange(location: r.lowerBound, length: string.count - r.lowerBound)
            check(&range)
            var dict : [NSAttributedString.Key: T] = [:]
            enumerateAttributes(in: range, options: .longestEffectiveRangeNotRequired) { (atts, range, pointer) in
                dict = atts as! [NSAttributedString.Key : T]
            }
            
            return dict
        }
        
        set {
            if let value = newValue {
                var range = NSRange(location: r.lowerBound, length: string.count - r.lowerBound)
                check(&range)
                value.forEach {
                    addAttribute($0, value: $1, range: range)
                }
            }
        }
        
    }
    
}

总结

上述 extension 的具体用法，看注释吧。

又水了一篇～（逃