Swift getting started tutorial 15-extension)

Swift getting started tutorial 15-extension)
 

1. extensions Definition
Extension is to add new functions to an existing class, struct, or enumeration. The extension does not need to obtain the source code of the original class.
The extension is similar to the categories in objective C.
Extended functions include

1. Calculation attributes and calculation static attributes (you cannot add storage attributes and attribute observation periods)
2. New instance method and type Method
3. Provide a new Constructor
4. Define the following table specimens
5. Define and use new nested types
6. Make existing types conform to a protocol

Syntax
Declared by the keyword extension

extension SomeType {// }

Scale to make it conform to a protocol

Extension SomeType: SomeProtocol, AnotherProctocol {// protocol implementation written here}

This part of the agreement will be explained later


Ii. extended String instance
If you are not familiar with String, refer to the article I wrote earlier.
Http://blog.csdn.net/hello_hwc/article/details/39853023
One example covers common extensions besides protocols

Extension String {// extended subscript script subscript (r: Range
 
  
)-> String {get {let subStart = advance (self. startIndex, r. startIndex, self. endIndex) let subEnd = advance (subStart, r. endIndex-r. startIndex, self. endIndex) return self. substringWithRange (Range (start: subStart, end: subEnd) }}// extended instance method func substring (# from: Int)-> String {let end = countElements (self) return self [from ..
  
   
String {let end = from + length return self [from ..
   
    
String {return self [from ..
    
     
Note: If you want to see the result, copy the code to palyground to see the result.