regular expression

1. Introduce
    Is an independent language , Applicable to all development languages , Even the editor
      1. Match scheme
        .   Match any character , Except for line breaks
        * Match any number of characters
        ?   Match as little as possible
       2. Common functions
         firstMatch In the specified string , lookup ‘ first ’ and pattern Match string
         matches In the specified string , Find all and pattern Matching string
       3. Common methods
           range(index)
           index = 0 Get all and pattern Matching is always a string
           index = 1 Fetch pattern in ( first ) Internal content , In turn, increasing
        4.pattern How to write
           1> Copy the complete string directly to pattern
           2> Use the content you need to get (.*?) Set up
           3> Will not care about the content , Variable content usage “.*?” Filter and ignore , It can adapt to more data matching
        5. Because regular expressions are applicable to all languages , Common regular expressions , You can search for

2. Create classification String+Regex.swift

import Foundation
extension String{
    /// From the current string , Filter links and text 
    /// Tuples , You can allow a function to return multiple values 
    func href() -> (link: String, text: String)?{
        // Create regular expression 
        // Match scheme  -  Specially used to filter strings 
        // throws   in the light of  patern  Whether the exception handling is correct 
        let pattern = "<a href=\"(.*?)\" .*?>(.*?)</a>"
        //throws  in the light of  pattern  Whether the exception handling is correct 
        let regex = try! NSRegularExpression(pattern: pattern, options: [])
        
        guard let result = regex.firstMatch(in: self, options: [], range: NSRange(location: 0, length: self.count)) else{
            print(" No matching items ")
            return nil
        }
        let str = (self as NSString)
        let r1 = result.range(at: 1)
        let link = str.substring(with: r1)
        let r2 = result.range(at: 2)
        let text = str.substring(with: r2)
        //print(link + "\n" + text)
        return (link,text)
    }
}

 3. The test method

let str = "aaaa zxzc <a href=\"http://app.baidu.com/t/feed/6vtZb0\" rel=\"nofollow\"> Baidu  baidu.com</a> asda"
print(str.href()?.link)
print(str.href()?.text)

4. Output results
Optional("http://app.baidu.com/t/feed/6vtZb0")
Optional(" Baidu baidu.com")