let count = 3

            for (i, answer) in answers.enumerated() {
                if _answers.isEmpty || i % count == 0 {
                    _answers.append([answer])
                } else {
                    _answers[i / count].append(answer)
                }
            }

响应链
http://hongchaozhang.github.io/blog/2015/10/21/touch-event-in-ios/
http://www.jianshu.com/p/12ef1c9f9741
http://zhoon.github.io/ios/2015/04/12/ios-event.html

版本比较

// 6.5.1 < 7.0
let flag = "6.5.1".compare("7.0", options: .numeric) == .orderedAscending
/// true

// 6.5.1 > 7.0
let flag = "6.5.1".compare("7.0", options: .numeric) == .orderedDescending
//  false

进位除法

(a + b - 1) / b

16进制字符串对100求余

let target = [
            76,
            16,
            56,
            96,
            36
        ]

        let str = "2131412EB552"
        var result = 0
        for (i, char) in str.reversed().enumerated() {
            let number = Int("\(char)", radix: 16)!
            if i == 0 {
                result = number
                continue
            }
            let idx = i % 5
            let n = target[idx]
            result += (number * n)
        }
        result %= 100

- (int)calculateHexMod:(NSString *)hexString {
    static NSArray <NSNumber *>*targets;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        targets = @[
                    @76,
                    @16,
                    @56,
                    @96,
                    @36
                    ];
    });

    int result = 0;
    NSInteger strLength = hexString.length;
    for (int i = 0; i < strLength; i++) {
        NSString *subStr = [hexString substringWithRange:NSMakeRange(strLength - 1 - i, 1)];
        int number = (int)strtoull([subStr UTF8String], NULL, 16);
        if (i == 0) {
            result = number;
            continue;
        }
        int idx = i % 5;
        int n = targets[idx].intValue;
        result += (number * n);
    }

    result %= 100;

    return result;
}

打印内存地址

let a = [1, 2, 3, 4]
var b = [1, 2, 3, 4]
print(address(o: a))
a.withUnsafeBufferPointer {
   print($0)
}
b.withUnsafeBufferPointer {
  print($0)
}
b.append(5)
b.withUnsafeBufferPointer {
  print($0)
}

func address(o: UnsafeRawPointer) -> String {
        return String(format: "%018p", Int(bitPattern: o))
    }

锁

Swift 中的锁和线程安全

iOS 开发中的八种锁

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Swift 中的锁和线程安全

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