I know what classes are about, but for better understanding I need a use case. Recently I discovered the construct of data classes. I get the idea behind normal classes, but I cannot imagine a real use case for data classes.
When should I use a data class and when I use a "normal" class? For all I know, all classes keep data.
Can you provide a good example that distinguishes data classes from non-data classes?
A data class is used to store data. It's lighter than a normal class, and can be compared to an array with key/value (dictionary, hash, etc.), but represented as an object with fixed attributes. In kotlin, according to the documentation, that adds those attributes to the class:
equals()/hashCode() pair
toString() of the form "User(name=John, age=42)"
componentN() functions corresponding to the properties in their order of declaration.
copy() function
Also it has a different behavior during class inheritence :
If there are explicit implementations of equals(), hashCode(), or toString() in the data class body or final implementations in a
superclass, then these functions are not generated, and the existing
implementations are used.
If a supertype has componentN() functions that are open and return compatible types, the corresponding functions are generated for the
data class and override those of the supertype. If the functions of
the supertype cannot be overridden due to incompatible signatures or
due to their being final, an error is reported.
Providing explicit implementations for the componentN() and copy() functions is not allowed.
So in kotlin, if you want to describe an object (a data) then you may use a dataclass, but if you're creating a complex application and your class needs to have special behavior in the constructor, with inheritence or abstraction, then you should use a normal class.
I do not know Kotlin, but in Python, a dataclass can be seen as a structured dict. When you want to use a dict to store an object which has always the same attributes, then you should not put it in a dict but use a Dataclass.
The advantage with a normal class is that you don't need to declare the __init__ method, as it is "automatic" (inherited).
Example :
This is a normal class
class Apple:
def __init__(size:int, color:str, sweet:bool=True):
self.size = size
self.color = color
self.sweet = sweet
Same class as a dataclass
from dataclasses import dataclass
#dataclass
class Apple:
size: int
color: str
sweet: bool = True
Then the advantage compared to a dict is that you are sure of what attribute it has. Also it can contains methods.
The advantage over to a normal class is that it is simpler to declare and make the code lighter. We can see that the attributes keywords (e.g size) are repeated 3 times in a normal class, but appear only once in a dataclass.
The advantage of normal class also is that you can personalize the __init__ method, (in a dataclass also, but then you lose it's main advantage I think) example:
# You need only 2 variable to initialize your class
class Apple:
def __init__(size:int, color:str):
self.size = size
self.color = color
# But you get much more info from those two.
self.sweet = True if color == 'red' else False
self.weight = self.__compute_weight()
self.price = self.weight * PRICE_PER_GRAM
def __compute_weight(self):
# ...
return (self.size**2)*10 # That's a random example
Abstractly, a data class is a pure, inert information record that doesn’t require any special handling when copied or passed around, and it represents nothing more than what is contained in its fields; it has no identity of its own. A typical example is a point in 3D space:
data class Point3D(
val x: Double,
val y: Double,
val z: Double
)
As long as the values are valid, an instance of a data class is entirely interchangeable with its fields, and it can be put apart or rematerialized at will. Often there is even little use for encapsulation: users of the data class can just access the instance’s fields directly. The Kotlin language provides a number of convenience features when data classes are declared as such in your code, which are described in the documentation. Those are useful when for example building more complex data structures employing data classes: you can for example have a hashmap assign values to particular points in space, and then be able to look up the value using a newly-constructed Point3D.
val map = HashMap<Point3D, String>()
map.set(Point3D(3, 4, 5), "point of interest")
println(map.get(Point3D(3, 4, 5))) // prints "point of interest"
For an example of a class that is not a data class, take FileReader. Underneath, this class probably keeps some kind of file handle in a private field, which you can assume to be an integer (as it actually is on at least some platforms). But you cannot expect to store this integer in a database, have another process read that same integer from the database, reconstruct a FileReader from it and expect it to work. Passing file handles between processes requires more ceremony than that, if it is even possible on a given platform. That property makes FileReader not a data class. Many examples of non-data classes will be of this kind: any class whose instances represent transient, local resources like a network connection, a position within a file or a running process, cannot be a data class. Likewise, any class where different instances should not be considered equal even if they contain the same information is not a data class either.
From the comments, it sounds like your question is really about why non-data classes exist in Kotlin and why you would ever choose not to make a data class. Here are some reasons.
Data classes are a lot more restrictive than a regular class:
They have to have a primary constructor, and every parameter of the primary constructor has to be a property.
They cannot have an empty primary constructor.
They cannot be open so they cannot be subclassed.
Here are other reasons:
Sometimes you don't want a class to have a copy function. If a class holds onto some heavy state that is expensive to copy, maybe it shouldn't advertise that it should be copied by presenting a copy function.
Sometimes you want to use an instance of a class in a Set or as Map keys without two different instances being considered as equivalent just because their properties have the same values.
The features of data classes are useful specifically for simple data holders, so the drawbacks are often something you want to avoid.
Yeah, I'm struggling with that. I cannot distinguish among them because every explanation I read is so unclear and philosophical enough. Can someone clear up these definitions for me ? Thanks guys.
These definitions apply as much to procedural-programming as oop ? Thanks.
Over time, the way people use each of these terms has changed (and will likely keep changing), but here's what they probably mean if you're reading articles written in the last decade or so:
Functions (aka subroutines) are relatively self-contained, relatively independent pieces of code that make up a larger program.
Methods are functions attached to specific classes (or instances) in object-oriented programming.
Properties are an object-oriented idiom. The term describes a one or two functions (depending on the desired program behavior) - a 'getter' that retrieves a value and a 'setter' that sets a value. By convention, properties usually don't have many side-effects. (And the side-effects they do have usually have limited scope: they may validate the item being set, notify listeners of a change, or convert an object's private data to or from a publicly-declared type.)
Function is a combination of instructions coupled together to achieve some result. It may take arguments and return result. If a function doesn't return a result it is usually called a procedure. Examples:
function drawLine(x1, y1, x2, y2):
// draws a line using Bresenham's algorithm from x1,y1 to x2,y2.
// doesn't return anything
function <number> add(a, b):
// adds a to b and returns the result as a number
return a + b
So functions are to do some particular work. For example, when you need to draw a polygon of 3 lines as a part of a vector image it is more convenient to call drawLine thrice than to put all the routine for line drawing inline.
Methods ("member functions") are similar to functions, they belongs to classes or objects and usually expresses the verbs of the objects/class. For example, an object of type Window usually would have methods open and close which do corresponding operations to the object they belong.
Properties are as in everyday language and technically are fields of objects/classes with dedicated getter/setter routines (which can be considered as methods. There are languages that don't have properties and this behavior is achieved using a private field+get/set methods.).
Field - A field is a variable of any type that is declared directly in a class or struct. Fields are members of their containing type.
Property - A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field.
Method - A method is a code block containing a series of statements. In C#, every executed instruction is done so in the context of a method.
Procedure - A procedure is a code block containing a series of statements.
Function - A function is a code block containing a series of statements. That return operation result.
Function is a standalone construction like trim(), strlen(), fopen() etc.
function myAbcFunction() { ... }
Method is a function of object. It is defined in class. Property is just property of object:
class MyClass {
public $property; // Public property: $objInstance->property
protected $property2; // Protected property
public function doSth() {
// That's a method. $objInstance->doSth();
}
}
I suggest read the manual Classes and Objects chapter.
In OOP the primary structure is an object.
Method is a named action which can be applied to the object.
Property is a named value, which the object has. For example, object Human has the property 'Age'.
function is a more general thing, than a method. It is just an action, that doesn't belong to any object. But method is a function that belongs to the object.
a)Function
Refers to block of statements that perform a particular task and return a value.
b)Procedure
Refers to the building blocks of a program that do not return a value when called.
c)Method
Refers to the action that object can perform.
Can someone provide a simple explanation of methods vs. functions in OOP context?
A function is a piece of code that is called by name. It can be passed data to operate on (i.e. the parameters) and can optionally return data (the return value). All data that is passed to a function is explicitly passed.
A method is a piece of code that is called by a name that is associated with an object. In most respects it is identical to a function except for two key differences:
A method is implicitly passed the object on which it was called.
A method is able to operate on data that is contained within the class (remembering that an object is an instance of a class - the class is the definition, the object is an instance of that data).
(this is a simplified explanation, ignoring issues of scope etc.)
A method is on an object or is static in class.
A function is independent of any object (and outside of any class).
For Java and C#, there are only methods.
For C, there are only functions.
For C++ and Python it would depend on whether or not you're in a class.
But in basic English:
Function: Standalone feature or functionality.
Method: One way of doing something, which has different approaches or methods, but related to the same aspect (aka class).
'method' is the object-oriented word for 'function'. That's pretty much all there is to it (ie., no real difference).
Unfortunately, I think a lot of the answers here are perpetuating or advancing the idea that there's some complex, meaningful difference.
Really - there isn't all that much to it, just different words for the same thing.
[late addition]
In fact, as Brian Neal pointed out in a comment to this question, the C++ standard never uses the term 'method' when refering to member functions. Some people may take that as an indication that C++ isn't really an object-oriented language; however, I prefer to take it as an indication that a pretty smart group of people didn't think there was a particularly strong reason to use a different term.
In general: methods are functions that belong to a class, functions can be on any other scope of the code so you could state that all methods are functions, but not all functions are methods:
Take the following python example:
class Door:
def open(self):
print 'hello stranger'
def knock_door():
a_door = Door()
Door.open(a_door)
knock_door()
The example given shows you a class called "Door" which has a method or action called "open", it is called a method because it was declared inside a class. There is another portion of code with "def" just below which defines a function, it is a function because it is not declared inside a class, this function calls the method we defined inside our class as you can see and finally the function is being called by itself.
As you can see you can call a function anywhere but if you want to call a method either you have to pass a new object of the same type as the class the method is declared (Class.method(object)) or you have to invoke the method inside the object (object.Method()), at least in python.
Think of methods as things only one entity can do, so if you have a Dog class it would make sense to have a bark function only inside that class and that would be a method, if you have also a Person class it could make sense to write a function "feed" for that doesn't belong to any class since both humans and dogs can be fed and you could call that a function since it does not belong to any class in particular.
Simple way to remember:
Function → Free (Free means it can be anywhere, no need to be in an object or class)
Method → Member (A member of an object or class)
A very general definition of the main difference between a Function and a Method:
Functions are defined outside of classes, while Methods are defined inside of and part of classes.
The idea behind Object Oriented paradigm is to "treat" the software is composed of .. well "objects". Objects in real world have properties, for instance if you have an Employee, the employee has a name, an employee id, a position, he belongs to a department etc. etc.
The object also know how to deal with its attributes and perform some operations on them. Let say if we want to know what an employee is doing right now we would ask him.
employe whatAreYouDoing.
That "whatAreYouDoing" is a "message" sent to the object. The object knows how to answer to that questions, it is said it has a "method" to resolve the question.
So, the way objects have to expose its behavior are called methods. Methods thus are the artifact object have to "do" something.
Other possible methods are
employee whatIsYourName
employee whatIsYourDepartmentsName
etc.
Functions in the other hand are ways a programming language has to compute some data, for instance you might have the function addValues( 8 , 8 ) that returns 16
// pseudo-code
function addValues( int x, int y ) return x + y
// call it
result = addValues( 8,8 )
print result // output is 16...
Since first popular programming languages ( such as fortran, c, pascal ) didn't cover the OO paradigm, they only call to these artifacts "functions".
for instance the previous function in C would be:
int addValues( int x, int y )
{
return x + y;
}
It is not "natural" to say an object has a "function" to perform some action, because functions are more related to mathematical stuff while an Employee has little mathematic on it, but you can have methods that do exactly the same as functions, for instance in Java this would be the equivalent addValues function.
public static int addValues( int x, int y ) {
return x + y;
}
Looks familiar? That´s because Java have its roots on C++ and C++ on C.
At the end is just a concept, in implementation they might look the same, but in the OO documentation these are called method.
Here´s an example of the previously Employee object in Java.
public class Employee {
Department department;
String name;
public String whatsYourName(){
return this.name;
}
public String whatsYourDeparmentsName(){
return this.department.name();
}
public String whatAreYouDoing(){
return "nothing";
}
// Ignore the following, only set here for completness
public Employee( String name ) {
this.name = name;
}
}
// Usage sample.
Employee employee = new Employee( "John" ); // Creates an employee called John
// If I want to display what is this employee doing I could use its methods.
// to know it.
String name = employee.whatIsYourName():
String doingWhat = employee.whatAreYouDoint();
// Print the info to the console.
System.out.printf("Employee %s is doing: %s", name, doingWhat );
Output:
Employee John is doing nothing.
The difference then, is on the "domain" where it is applied.
AppleScript have the idea of "natural language" matphor , that at some point OO had. For instance Smalltalk. I hope it may be reasonable easier for you to understand methods in objects after reading this.
NOTE: The code is not to be compiled, just to serve as an example. Feel free to modify the post and add Python example.
In OO world, the two are commonly used to mean the same thing.
From a pure Math and CS perspective, a function will always return the same result when called with the same arguments ( f(x,y) = (x + y) ). A method on the other hand, is typically associated with an instance of a class. Again though, most modern OO languages no longer use the term "function" for the most part. Many static methods can be quite like functions, as they typically have no state (not always true).
Let's say a function is a block of code (usually with its own scope, and sometimes with its own closure) that may receive some arguments and may also return a result.
A method is a function that is owned by an object (in some object oriented systems, it is more correct to say it is owned by a class). Being "owned" by a object/class means that you refer to the method through the object/class; for example, in Java if you want to invoke a method "open()" owned by an object "door" you need to write "door.open()".
Usually methods also gain some extra attributes describing their behaviour within the object/class, for example: visibility (related to the object oriented concept of encapsulation) which defines from which objects (or classes) the method can be invoked.
In many object oriented languages, all "functions" belong to some object (or class) and so in these languages there are no functions that are not methods.
Methods are functions of classes. In normal jargon, people interchange method and function all over. Basically you can think of them as the same thing (not sure if global functions are called methods).
http://en.wikipedia.org/wiki/Method_(computer_science)
A function is a mathematical concept. For example:
f(x,y) = sin(x) + cos(y)
says that function f() will return the sin of the first parameter added to the cosine of the second parameter. It's just math. As it happens sin() and cos() are also functions. A function has another property: all calls to a function with the same parameters, should return the same result.
A method, on the other hand, is a function that is related to an object in an object-oriented language. It has one implicit parameter: the object being acted upon (and it's state).
So, if you have an object Z with a method g(x), you might see the following:
Z.g(x) = sin(x) + cos(Z.y)
In this case, the parameter x is passed in, the same as in the function example earlier. However, the parameter to cos() is a value that lives inside the object Z. Z and the data that lives inside it (Z.y) are implicit parameters to Z's g() method.
Historically, there may have been a subtle difference with a "method" being something which does not return a value, and a "function" one which does.Each language has its own lexicon of terms with special meaning.
In "C", the word "function" means a program routine.
In Java, the term "function" does not have any special meaning. Whereas "method" means one of the routines that forms the implementation of a class.
In C# that would translate as:
public void DoSomething() {} // method
public int DoSomethingAndReturnMeANumber(){} // function
But really, I re-iterate that there is really no difference in the 2 concepts.
If you use the term "function" in informal discussions about Java, people will assume you meant "method" and carry on. Don't use it in proper documents or presentations about Java, or you will look silly.
Function or a method is a named callable piece of code which performs some operations and optionally returns a value.
In C language the term function is used. Java & C# people would say it a method (and a function in this case is defined within a class/object).
A C++ programmer might call it a function or sometimes method (depending on if they are writing procedural style c++ code or are doing object oriented way of C++, also a C/C++ only programmer would likely call it a function because term 'method' is less often used in C/C++ literature).
You use a function by just calling it's name like,
result = mySum(num1, num2);
You would call a method by referencing its object first like,
result = MyCalc.mySum(num1,num2);
Function is a set of logic that can be used to manipulate data.
While, Method is function that is used to manipulate the data of the object where it belongs.
So technically, if you have a function that is not completely related to your class but was declared in the class, its not a method; It's called a bad design.
In OO languages such as Object Pascal or C++, a "method" is a function associated with an object. So, for example, a "Dog" object might have a "bark" function and this would be considered a "Method". In contrast, the "StrLen" function stands alone (it provides the length of a string provided as an argument). It is thus just a "function." Javascript is technically Object Oriented as well but faces many limitations compared to a full-blown language like C++, C# or Pascal. Nonetheless, the distinction should still hold.
A couple of additional facts: C# is fully object oriented so you cannot create standalone "functions." In C# every function is bound to an object and is thus, technically, a "method." The kicker is that few people in C# refer to them as "methods" - they just use the term "functions" because there isn't any real distinction to be made.
Finally - just so any Pascal gurus don't jump on me here - Pascal also differentiates between "functions" (which return a value) and "procedures" which do not. C# does not make this distinction explicitly although you can, of course, choose to return a value or not.
Methods on a class act on the instance of the class, called the object.
class Example
{
public int data = 0; // Each instance of Example holds its internal data. This is a "field", or "member variable".
public void UpdateData() // .. and manipulates it (This is a method by the way)
{
data = data + 1;
}
public void PrintData() // This is also a method
{
Console.WriteLine(data);
}
}
class Program
{
public static void Main()
{
Example exampleObject1 = new Example();
Example exampleObject2 = new Example();
exampleObject1.UpdateData();
exampleObject1.UpdateData();
exampleObject2.UpdateData();
exampleObject1.PrintData(); // Prints "2"
exampleObject2.PrintData(); // Prints "1"
}
}
Since you mentioned Python, the following might be a useful illustration of the relationship between methods and objects in most modern object-oriented languages. In a nutshell what they call a "method" is just a function that gets passed an extra argument (as other answers have pointed out), but Python makes that more explicit than most languages.
# perfectly normal function
def hello(greetee):
print "Hello", greetee
# generalise a bit (still a function though)
def greet(greeting, greetee):
print greeting, greetee
# hide the greeting behind a layer of abstraction (still a function!)
def greet_with_greeter(greeter, greetee):
print greeter.greeting, greetee
# very simple class we can pass to greet_with_greeter
class Greeter(object):
def __init__(self, greeting):
self.greeting = greeting
# while we're at it, here's a method that uses self.greeting...
def greet(self, greetee):
print self.greeting, greetee
# save an object of class Greeter for later
hello_greeter = Greeter("Hello")
# now all of the following print the same message
hello("World")
greet("Hello", "World")
greet_with_greeter(hello_greeter, "World")
hello_greeter.greet("World")
Now compare the function greet_with_greeter and the method greet: the only difference is the name of the first parameter (in the function I called it "greeter", in the method I called it "self"). So I can use the greet method in exactly the same way as I use the greet_with_greeter function (using the "dot" syntax to get at it, since I defined it inside a class):
Greeter.greet(hello_greeter, "World")
So I've effectively turned a method into a function. Can I turn a function into a method? Well, as Python lets you mess with classes after they're defined, let's try:
Greeter.greet2 = greet_with_greeter
hello_greeter.greet2("World")
Yes, the function greet_with_greeter is now also known as the method greet2. This shows the only real difference between a method and a function: when you call a method "on" an object by calling object.method(args), the language magically turns it into method(object, args).
(OO purists might argue a method is something different from a function, and if you get into advanced Python or Ruby - or Smalltalk! - you will start to see their point. Also some languages give methods special access to bits of an object. But the main conceptual difference is still the hidden extra parameter.)
for me:
the function of a method and a function is the same if I agree that:
a function may return a value
may expect parameters
Just like any piece of code you may have objects you put in and you may have an object that comes as a result. During doing that they might change the state of an object but that would not change their basic functioning for me.
There might be a definition differencing in calling functions of objects or other codes. But isn't that something for a verbal differenciations and that's why people interchange them? The mentions example of computation I would be careful with. because I hire employes to do my calculations:
new Employer().calculateSum( 8, 8 );
By doing it that way I can rely on an employer being responsible for calculations. If he wants more money I free him and let the carbage collector's function of disposing unused employees do the rest and get a new employee.
Even arguing that a method is an objects function and a function is unconnected computation will not help me. The function descriptor itself and ideally the function's documentation will tell me what it needs and what it may return. The rest, like manipulating some object's state is not really transparent to me. I do expect both functions and methods to deliver and manipulate what they claim to without needing to know in detail how they do it.
Even a pure computational function might change the console's state or append to a logfile.
From my understanding a method is any operation which can be performed on a class. It is a general term used in programming.
In many languages methods are represented by functions and subroutines. The main distinction that most languages use for these is that functions may return a value back to the caller and a subroutine may not. However many modern languages only have functions, but these can optionally not return any value.
For example, lets say you want to describe a cat and you would like that to be able to yawn. You would create a Cat class, with a Yawn method, which would most likely be a function without any return value.
To a first order approximation, a method (in C++ style OO) is another word for a member function, that is a function that is part of a class.
In languages like C/C++ you can have functions which are not members of a class; you don't call a function not associated with a class a method.
IMHO people just wanted to invent new word for easier communication between programmers when they wanted to refer to functions inside objects.
If you are saying methods you mean functions inside the class.
If you are saying functions you mean simply functions outside the class.
The truth is that both words are used to describe functions. Even if you used it wrongly nothing wrong happens. Both words describe well what you want to achieve in your code.
Function is a code that has to play a role (a function) of doing something.
Method is a method to resolve the problem.
It does the same thing. It is the same thing. If you want to be super precise and go along with the convention you can call methods as the functions inside objects.
Let's not over complicate what should be a very simple answer. Methods and functions are the same thing. You call a function a function when it is outside of a class, and you call a function a method when it is written inside a class.
Function is the concept mainly belonging to Procedure oriented programming where a function is an an entity which can process data and returns you value
Method is the concept of Object Oriented programming where a method is a member of a class which mostly does processing on the class members.
I am not an expert, but this is what I know:
Function is C language term, it refers to a piece of code and the function name will be the identifier to use this function.
Method is the OO term, typically it has a this pointer in the function parameter. You can not invoke this piece of code like C, you need to use object to invoke it.
The invoke methods are also different. Here invoke meaning to find the address of this piece of code. C/C++, the linking time will use the function symbol to locate.
Objecive-C is different. Invoke meaning a C function to use data structure to find the address. It means everything is known at run time.
TL;DR
A Function is a piece of code to run.
A Method is a Function inside an Object.
Example of a function:
function sum(){
console.log("sum")l
}
Example of a Method:
const obj = {
a:1,
b:2,
sum(){
}
}
So thats why we say that a "this" keyword inside a Function is not very useful unless we use it with call, apply or bind .. because call, apply, bind will call that function as a method inside object ==> basically it converts function to method
I know many others have already answered, but I found following is a simple, yet effective single line answer. Though it doesn't look a lot better than others answers here, but if you read it carefully, it has everything you need to know about the method vs function.
A method is a function that has a defined receiver, in OOP terms, a method is a function on an instance of an object.
A class is the collection of some data and function optionally with a constructor.
While you creating an instance (copy,replication) of that particular class the constructor initialize the class and return an object.
Now the class become object (without constructor)
&
Functions are known as method in the object context.
So basically
Class <==new==>Object
Function <==new==>Method
In java the it is generally told as that the constructor name same as class name but in real that constructor is like instance block and static block but with having a user define return type(i.e. Class type)
While the class can have an static block,instance block,constructor, function
The object generally have only data & method.
Function - A function in an independent piece of code which includes some logic and must be called independently and are defined outside of class.
Method - A method is an independent piece of code which is called in reference to some object and are be defined inside the class.
General answer is:
method has object context (this, or class instance reference),
function has none context (null, or global, or static).
But answer to question is dependent on terminology of language you use.
In JavaScript (ES 6) you are free to customising function context (this) for any you desire, which is normally must be link to the (this) object instance context.
In Java world you always hear that "only OOP classes/objects, no functions", but if you watch in detailes to static methods in Java, they are really in global/null context (or context of classes, whithout instancing), so just functions whithout object. Java teachers could told you, that functions were rudiment of C in C++ and dropped in Java, but they told you it for simplification of history and avoiding unnecessary questions of newbies. If you see at Java after 7 version, you can find many elements of pure function programming (even not from C, but from older 1988 Lisp) for simplifying parallel computing, and it is not OOP classes style.
In C++ and D world things are stronger, and you have separated functions and objects with methods and fields. But in practice, you again see functions without this and methods whith this (with object context).
In FreePascal/Lazarus and Borland Pascal/Delphi things about separation terms of functions and objects (variables and fields) are usually similar to C++.
Objective-C comes from C world, so you must separate C functions and Objective-C objects with methods addon.
C# is very similar to Java, but has many C++ advantages.
In C++, sometimes, method is used to reflect the notion of member function of a class. However, recently I found a statement in the book «The C++ Programming Language 4th Edition», on page 586 "Derived Classes"
A virtual function is sometimes called a method.
This is a little bit confusing, but he said sometimes, so it roughly makes sense, C++ creator tends to see methods as functions can be invoked on objects and can behave polymorphic.