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In Objective-C, for example, both the generic Object and NSObject (in Cocoa/OpenStep) provide the method isMemberOfClass: which returns true if the argument to the method is an instance of the specified class. The method isKindOfClass: analogously returns true if the argument inherits from the specified class.
Java [4] all non-object types, including (e.g.) booleans and numbers: all object types, including (e.g.) arrays C++: all data types, except reference types, array types and function types: arrays and functions C# [5] all non-object types, including structures and enumerations as well as primitive types: all object-types, including both classes ...
Python has data classes which provides equality testing and can be made immutable using the frozen parameter. [21] It overrides the __str__ dunder method. [22] This example implementation includes a static method which can be used to initialize a new instance with a randomly generated universally unique identifier (UUID).
A class may have both instance variables and class variables. Instance variables can be used by all instance methods of an object, but may not be used by class methods. An instance variable may also be changed directly, provided access restrictions are set. [6]
The boolean values True and False were added to the language in Python 2.2.1 as constants (subclassed from 1 and 0) and were changed to be full blown keywords in Python 3. The binary comparison operators such as == and > return either True or False. The boolean operators and and or use minimal evaluation.
In Objective-C, the constructor method is split across two methods, "alloc" and "init" with the alloc method setting aside (allocating) memory for an instance of the class, and the init method handling the bulk of initializing the instance. A call to the method "new" invokes both the alloc and the init methods, for the class instance.
For function that manipulate strings, modern object-oriented languages, like C# and Java have immutable strings and return a copy (in newly allocated dynamic memory), while others, like C manipulate the original string unless the programmer copies data to a new string.
In another example, if Number, Rational, and Integer are types such that Number :> Rational and Number :> Integer (Rational and Integer as subtypes of a type Number that is a supertype of them), a function written to take a Number will work equally well when passed an Integer or Rational as when passed a Number. The actual type of the object ...