探寻iOS之协议（protocol）

A protocol declares a programmatic interface that any class may choose to implement. Protocols make it possible for two classes distantly related by inheritance to communicate with each other to accomplish a certain goal. They thus offer an alternative to subclassing. Any class that can provide behavior useful to other classes may declare a programmatic interface for vending that behavior anonymously. Any other class may choose to adopt the protocol and implement one or more of its methods, thereby making use of the behavior. The class that declares a protocol is expected to call the methods in the protocol if they are implemented by the protocol adopter.

协议是任何类都能够选择实现的程序接口。协议能够使两个没有继承关系的类相互交流并完成特定的目的，因此它提供了除继承外的另一种选择。任何能够为其他类提供有用行为的类都能够声明接口来匿名的传达这个行为。任何其他类都能够选择遵守这个协议并实现其中的一个或多个方法，从而利用这个行为。如果协议遵守者实现了协议中的方法，那么声明协议的类就能够通过遵守者调用协议中的方法。

@protocol MGSwipeTableCellDelegate <NSObject>
@optional

There are two varieties of protocol, formal and informal:

A formal protocol declares a list of methods that client classes are expected to implement. Formal protocols have their own declaration, adoption, and type-checking syntax. You can designate methods whose implementation is required or optional with the @required and @optional keywords. Subclasses inherit formal protocols adopted by their ancestors. A formal protocol can also adopt other protocols. Formal protocols are an extension to the Objective-C language.

An informal protocol is a category on NSObject, which implicitly makes almost all objects adopters of the protocol. (A category is a language feature that enables you to add methods to a class without subclassing it.) Implementation of the methods in an informal protocol is optional. Before invoking a method, the calling object checks to see whether the target object implements it. Until optional protocol methods were introduced in Objective-C 2.0, informal protocols were essential to the way Foundation and AppKit classes implemented delegation.

@interface NSString (CamelCase)  //类别  
-(NSString*) camelCaseString;    
@end    

@protocol NSObject

- (BOOL)isEqual:(id)object;
@property (readonly) NSUInteger hash;

@property (readonly) Class superclass;
- (Class)class OBJC_SWIFT_UNAVAILABLE("use 'anObject.dynamicType' instead");
- (instancetype)self;

- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;

- (BOOL)isProxy;

- (BOOL)isKindOfClass:(Class)aClass;
- (BOOL)isMemberOfClass:(Class)aClass;
- (BOOL)conformsToProtocol:(Protocol *)aProtocol;

- (BOOL)respondsToSelector:(SEL)aSelector;

- (instancetype)retain OBJC_ARC_UNAVAILABLE;
- (oneway void)release OBJC_ARC_UNAVAILABLE;
- (instancetype)autorelease OBJC_ARC_UNAVAILABLE;
- (NSUInteger)retainCount OBJC_ARC_UNAVAILABLE;

- (struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;

@property (readonly, copy) NSString *description;
@optional
@property (readonly, copy) NSString *debugDescription;

@end

@protocol NSCoding

- (void)encodeWithCoder:(NSCoder *)aCoder;
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder; // NS_DESIGNATED_INITIALIZER

@end

- (id)copyWithZone:(NSZone *)zone{    
        PersonModel *model = [[[self class] allocWithZone:zone] init];
        model.firstName = self.firstName;
        model.lastName  = self.lastName;
        //未公开的成员
     model->_nickName = _nickName;
     return model;
}

@protocol NSMutableCopying

- (id)mutableCopyWithZone:(nullable NSZone *)zone;

@end

NSArray *nameArray = @[@"Jim", @"Tom", @"David"];
NSArray *copyArray = [nameArray copy];
NSMutableArray *mutableCopyArray = [nameArray mutableCopy];
[mutableCopyArray addObject:@"Sam"];

// Objects which are safe to be encoded and decoded across privilege boundaries should adopt NSSecureCoding instead of NSCoding. Secure coders (those that respond YES to requiresSecureCoding) will only encode objects that adopt the NSSecureCoding protocol.
// NOTE: NSSecureCoding guarantees only that an archive contains the classes it claims. It makes no guarantees about the suitability for consumption by the receiver of the decoded content of the archive. Archived objects which  may trigger code evaluation should be validated independently by the consumer of the objects to verify that no malicious code is executed (i.e. by checking key paths, selectors etc. specified in the archive).

@protocol NSSecureCoding <NSCoding>
@required
// This property must return YES on all classes that allow secure coding. Subclasses of classes that adopt NSSecureCoding and override initWithCoder: must also override this method and return YES.
// The Secure Coding Guide should be consulted when writing methods that decode data.
#if FOUNDATION_SWIFT_SDK_EPOCH_AT_LEAST(8)
@property (class, readonly) BOOL supportsSecureCoding;
#else
+ (BOOL)supportsSecureCoding;
#endif
@end