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1. abs 返回数字的绝对值

数轴上的点到原点的距离叫做绝对值

abs(Int32)

        let number1 = abs(-12.4);
        
        let number2 = abs(-12);
        
        let number3 = abs(-13.0011 / 2);
  
        // print result: 12.4,12,6.50055

2. contains(sequence,element)

如果某个序列sequence（比如说一个数组）包含指定的元素element，则返回

true，否则返回false。

let languages = ["Swift","Objective-C"]
        
        let isInclude1 = languages.contains("Swift");
      
        let isInclude2 = languages.contains("Java");
 
        // print result : true false

学自:http://letsswift.com/2014/06/74-swift-library-functions/