equality

#TODO

equal identical

NSObject isEqual

Container class: deep comparison

overriding isEqual

• isEqualClassName
• call isEqualClassName in isEqual
• override hash

if isEqual: determines that two objects are equal, they must have the same hash value

NSString *a = @"a";
NSString *b = @"b";
a == b is true

use isequaltoString never use == for comparing strings. string interning

参考記事 http://nshipster.com/equality/ https://developer.apple.com/library/ios/documentation/general/conceptual/DevPedia-CocoaCore/ObjectComparison.html