Learn notes from scratch (Day 50)--extend calculated properties, methods

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You can extend calculated properties on the original type, including instance calculation properties and static computed properties. The definition of a computed property is added, as is the definition of a normal computed property.

Example Compute Properties Examples: In order to reduce traffic when programming on the network, the information returned from the server is not described, but is encoded, and then the encoding is converted locally to descriptive information. The following INT type extensions are defined for this purpose :

extension int {              / /define Extended     var errormessage : string {   //read-only computed properties of type int         var errorstr = ""          switch  (self)  {             case -7:            errorstr =  " No data. "        case -6:             errorStr =  "date is not entered. "        case -5:             errorStr =  "content is not entered. "        case -4:             errorstr =  "id not entered. "        case -3:             errorStr =  "Failed to access the data. "        case -2:             errorStr =  "Your account can insert up to 10 data. "        case -1:             errorStr =  "User does not exist, please register to http://51work6.com. "        default:             errorStr =  ""         }                        return errorstr    }}let message = ( -7) .errorMessage       //Gets the description information for the 7 encoding print ("Error code : -7 , error message : \ ( Message) ")

Note the entire -7 including the minus sign is a complete instance, so calling its properties requires -7 enclosed in parentheses as a whole. However, if you are 7 , you do not need parentheses.

Let's look at a static Property Example:

struct account {              //defining the account structure body     var amount : double  = 0.0               // Account amount     var owner : String =  ""                   //Account name} extension account  {          //define an extended static      of the account structure body static var interestrate : double {      //rates           return0.0668    }} print ( account.interestrate)   //Print output InterestRate properties 

Print Output InterestRate property, accessed in the same way as other static computed properties, by the "type name" Plus " . to access the static computed properties.

Extension methods

You can extend methods on the original type, including instance methods and static methods. The definition of these additions is the same as for the normal method.

Let's look at an example below:

extension double {//defines the extension     static var interestrate&nbsp of the Double type;:  double = 0.0668//interest Rate     func interestby1 ()  -> Double  {                return  self * double.interestrate  //static property interest rate     }     mutating func interestby2 ()  {    //defines an instance method interestby2         self = self * Double.interestRate       }    static func interestby3 (amount : Double)  - > double {  //defining a static method Interestby3        return  interestrate * amount       //return value is calculated interest result      }} let interest1 =  (10_000.00). InterestBy1 ()     //call interestBy1 method to calculate interest print ("Interest 1 :\ (Interest1)" )  var interest2 = 10_000.00    // Call the InterestBy2 method to calculate the interest Interest2.interestby2 ()   print ("Interest 2 :\ (INTEREST2)")  var interest3  = double.interestby3 (10_000.00)     //calls the InterestBy3 method to calculate interest print ("Interest 3 :\ ( INTEREST3) ")

Code Self = self *double.interestrate To assign the result directly to the current instance Self . Assigning self to self in structs and enum types has a compile error, and you need to precede the method with the mutating keyword, which indicates that this is a mutation method.

call method calculates interest, invokes its instance 10_ 000.00 interest1

call method to calculate interest, we cannot use 10_ 000.00 instance calls, but requires a double interest2 interestby2 is the mutation method that directly alters the variable interest2 interest2.interestby2 () After the statement call is complete, the variable interest2 The value of

called InterestBy3 method calculates the interest, which is a static method that calls it to "type name . "The way that is" Double. "in the way called.

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Learn notes from scratch (Day 50)--extend calculated properties, methods