看了下别人的源码，发现有一个这样的写法我不大熟悉，原来是Swift中的Access Control。

  public final class Map {
  	public let mappingType: MappingType
  	
 -	var JSONDictionary: [String : AnyObject] = [:]
 +	public internal(set) var JSONDictionary: [String : AnyObject] = [:]
  	public var currentValue: AnyObject?
  	var currentKey: String?
  	var keyIsNested = false
 
@@ -157,4 +157,4 @@ private func valueFor(keyPathComponents: ArraySlice<String>, dictionary: [AnyObj
  	}
  	
  	return nil
 -}  
 +}

其中:

public internal(set) var JSONDictionary: [String : AnyObject] = [:]

书上是这样定义的：

  • Public access enables entities to be used within any source file from their defining module, and also in a source file from another module that imports the defining module. You typically use public access when specifying the public interface to a framework.
  • Internal access enables entities to be used within any source file from their defining module, but not in any source file outside of that module. You typically use internal access when defining an app’s or a framework’s internal structure.
  • Private access restricts the use of an entity to its own defining source file. Use private access to hide the implementation details of a specific piece of functionality.

Getters and Setters

Getters and setters for constants, variables, properties, and subscripts automatically receive the same access level as the constant, variable, property, or subscript they belong to.

You can give a setter a lower access level than its corresponding getter, to restrict the read-write scope of that variable, property, or subscript. You assign a lower access level by writing private(set) or internal(set) before the var or subscript introducer.

大概的意思就是如果要公开Getter方法给别人,可以这样定义API

public internal(set) var someproperty

通过internal(set)把Setter的访问权限设置成internal级别，就可以保护Setter 不被公开出去。