#Private attribute example
class C {
has $!w; #private attribute
multi method w { $!w } #getter method
multi method w ( $_ ) { #setter method
warn “Don’t go changing my w!”; #some side action
$!w = $_
}
}
my $c = C.new
$c.w( 42 )
say $c.w #prints 42
$c.w: 43
say $c.w #prints 43
#but not
$c.w = 44
Cannot modify an immutable Int (43)
so far, so reasonable, and then
#Public attribute example
class C {
has $.v is rw #public attribute with automatic accessors
}
my $c = C.new
$c.v = 42
say $c.v #prints 42
#but not
$c.v( 43 ) #or $c.v: 43
Too many positionals passed; expected 1 argument but got 2
I like the immediacy of the ‘=‘ assignment, but I need the ease of bunging in side actions that multi methods provide. I understand that these are two different worlds, and that they do not mix.
BUT - I do not understand why I can’t just go
$c.v( 43 )
To set a public attribute
I feel that raku is guiding me to not mix these two modes - some attributes private and some public and that the pressure is towards the method method (with some : sugar from the colon) - is this the intent of Raku's design?
Am I missing something?
is this the intent of Raku's design?
It's fair to say that Raku isn't entirely unopinionated in this area. Your question touches on two themes in Raku's design, which are both worth a little discussion.
Raku has first-class l-values
Raku makes plentiful use of l-values being a first-class thing. When we write:
has $.x is rw;
The method that is generated is:
method x() is rw { $!x }
The is rw here indicates that the method is returning an l-value - that is, something that can be assigned to. Thus when we write:
$obj.x = 42;
This is not syntactic sugar: it really is a method call, and then the assignment operator being applied to the result of it. This works out, because the method call returns the Scalar container of the attribute, which can then be assigned into. One can use binding to split this into two steps, to see it's not a trivial syntactic transform. For example, this:
my $target := $obj.x;
$target = 42;
Would be assigning to the object attribute. This same mechanism is behind numerous other features, including list assignment. For example, this:
($x, $y) = "foo", "bar";
Works by constructing a List containing the containers $x and $y, and then the assignment operator in this case iterates each side pairwise to do the assignment. This means we can use rw object accessors there:
($obj.x, $obj.y) = "foo", "bar";
And it all just naturally works. This is also the mechanism behind assigning to slices of arrays and hashes.
One can also use Proxy in order to create an l-value container where the behavior of reading and writing it are under your control. Thus, you could put the side-actions into STORE. However...
Raku encourages semantic methods over "setters"
When we describe OO, terms like "encapsulation" and "data hiding" often come up. The key idea here is that the state model inside the object - that is, the way it chooses to represent the data it needs in order to implement its behaviors (the methods) - is free to evolve, for example to handle new requirements. The more complex the object, the more liberating this becomes.
However, getters and setters are methods that have an implicit connection with the state. While we might claim we're achieving data hiding because we're calling a method, not accessing state directly, my experience is that we quickly end up at a place where outside code is making sequences of setter calls to achieve an operation - which is a form of the feature envy anti-pattern. And if we're doing that, it's pretty certain we'll end up with logic outside of the object that does a mix of getter and setter operations to achieve an operation. Really, these operations should have been exposed as methods with a names that describes what is being achieved. This becomes even more important if we're in a concurrent setting; a well-designed object is often fairly easy to protect at the method boundary.
That said, many uses of class are really record/product types: they exist to simply group together a bunch of data items. It's no accident that the . sigil doesn't just generate an accessor, but also:
Opts the attribute into being set by the default object initialization logic (that is, a class Point { has $.x; has $.y; } can be instantiated as Point.new(x => 1, y => 2)), and also renders that in the .raku dumping method.
Opts the attribute into the default .Capture object, meaning we can use it in destructuring (e.g. sub translated(Point (:$x, :$y)) { ... }).
Which are the things you'd want if you were writing in a more procedural or functional style and using class as a means to define a record type.
The Raku design is not optimized for doing clever things in setters, because that is considered a poor thing to optimize for. It's beyond what's needed for a record type; in some languages we could argue we want to do validation of what's being assigned, but in Raku we can turn to subset types for that. At the same time, if we're really doing an OO design, then we want an API of meaningful behaviors that hides the state model, rather than to be thinking in terms of getters/setters, which tend to lead to a failure to colocate data and behavior, which is much of the point of doing OO anyway.
BUT - I do not understand why I can’t just go $c.v( 43 ) To set a public attribute
Well, that's really up to the architect. But seriously, no, that's simply not the standard way Raku works.
Now, it would be entirely possible to create an Attribute trait in module space, something like is settable, that would create an alternate accessor method that would accept a single value to set the value. The problem with doing this in core is, is that I think there are basically 2 camps in the world about the return value of such a mutator: would it return the new value, or the old value?
Please contact me if you're interested in implementing such a trait in module space.
I currently suspect you just got confused.1 Before I touch on that, let's start over with what you're not confused about:
I like the immediacy of the = assignment, but I need the ease of bunging in side actions that multi methods provide. ... I do not understand why I can’t just go $c.v( 43 ) To set a public attribute
You can do all of these things. That is to say you use = assignment, and multi methods, and "just go $c.v( 43 )", all at the same time if you want to:
class C {
has $!v;
multi method v is rw { $!v }
multi method v ( :$trace! ) is rw { say 'trace'; $!v }
multi method v ( $new-value ) { say 'new-value'; $!v = $new-value }
}
my $c = C.new;
$c.v = 41;
say $c.v; # 41
$c.v(:trace) = 42; # trace
say $c.v; # 42
$c.v(43); # new-value
say $c.v; # 43
A possible source of confusion1
Behind the scenes, has $.foo is rw generates an attribute and a single method along the lines of:
has $!foo;
method foo () is rw { $!foo }
The above isn't quite right though. Given the behavior we're seeing, the compiler's autogenerated foo method is somehow being declared in such a way that any new method of the same name silently shadows it.2
So if you want one or more custom methods with the same name as an attribute you must manually replicate the automatically generated method if you wish to retain the behavior it would normally be responsible for.
Footnotes
1 See jnthn's answer for a clear, thorough, authoritative accounting of Raku's opinion about private vs public getters/setters and what it does behind the scenes when you declare public getters/setters (i.e. write has $.foo).
2 If an autogenerated accessor method for an attribute was declared only, then Raku would, I presume, throw an exception if a method with the same name was declared. If it were declared multi, then it should not be shadowed if the new method was also declared multi, and should throw an exception if not. So the autogenerated accessor is being declared with neither only nor multi but instead in some way that allows silent shadowing.
I've always known what static methods are by definition, but I've always avoided using them at school because I was afraid of what I didn't know.
I already understand that you can use it as a counter throughout your entire project.
Now that I am interning I want to know when exactly static methods are used. From my observation so far, static classes/methods are used when it contains a lot of functions that will be used in many different classes and itself doesn't contain too many critical local variables within the class where it is not necessary to create an instant of it.
So as an example, you can have a static class called Zip that zips and unzips files and provide it to many different classes for them to do whatever with it.
Am I right? Do I have the right idea? I'm pretty sure there are many ways to use it.
Static functions are helpful as they do not rely on an instantiated member of whatever class they are attached to.
Static functions can provide functionality related to an a particular class without requiring the programmer to first create an instance of that class.
See this comparison:
class Numbers
{
public int Add(int x, int y)
{
return x + y;
}
public static int AddNumbers(int x, int y)
{
return x + y;
}
}
class Main
{
//in this first case, we use the non-static version of the Add function
int z1 = (new Numbers()).Add(2, 4);
//in the second case, we use the static one
int z2 = Numbers.AddNumbers(3, 5);
}
Technically, answers above are correct.
But the examples are not correct from the OOP point of view.
For example you have a class like this:
class Zip
{
public static function zipFile($fileName)
{
//
}
public static function unzipFile($fileName)
{
//
}
}
The truth is that there is nothing object-oriented here. You just defined two functions which you need to call using the fancy syntax like Zip::zipFile($myFile) instead of just zipFile($myFile).
You don't create any objects here and the Zip class is only used as a namespace.
So in this case it is better to just define these functions outside of class, as regular functions. There are namespaces in php since version 5.3, you can use them if you want to group your functions.
With the OOP approach, your class would look like this:
class ZipArchive
{
private $_archiveFileName;
private $_files;
public function __construct($archiveFileName) {
$this->_archiveFileName = $archiveFileName;
$this->_files = [];
}
public function add($fileName)
{
$this->_files[] = $fileName;
return $this; // allows to chain calls
}
public function zip()
{
// zip the files into archive specified
// by $_archiveFileName
}
}
And then you can use it like this:
$archive = new ZipArchive('path/to/archive.zip');
$archive->add('file1')->add('file2')->zip();
What is more important, you can now use the zip functionality in an OOP way.
For example, you can have a base class Archive and sub-classes like ZipArchive, TarGzArchive, etc.
Now, you can create an instance of the specific sub-class and pass it to other code which will not even know if files are going to be zip-ped or tag.gz-ipped. For example:
if ($config['archive_type'] === 'targz') {
// use tar.gz if specified
$archive = new TarGzArchive($path);
} else {
// use zip by default
$archive = new ZipArchive($path);
}
$backup = new Backup($archive /*, other params*/);
$backup->run();
Now the $backup object will use the specified archive type. Internally it doesn't know and doesn't care how exactly files will be archived.
You can even have a CopyArchive class which will simply copy files to another location.
It is easy to do it this way because your archive support is written in OOP way. You have small object responsible for specific things, you create and combine them and get the result you want.
And if you just have a bunch of static methods instead of real class, you will be forced to write the procedural-style code.
So I would not recommend to use static methods to implement actual features of your application.
Static methods may be helpful to support logging, debugging, testing and similar things. Like if you want to count number of objects created, you can use class-level static counter, increment it in the constructor and you can have a static method which reads the counter and prints it or writes to the log file.
Yes, static classes are used for problems that require stateless computation. Such as adding two numbers. Zipping a file. Etc.
If your class requires state, where you need to store connections or other longer living entities, then you wouldn't use static.
AFAIK. Static methods does not depends on a class instance. Just that.
As an example:
If you have an single thread program that will have only ONE database connection and will do several queries against the database it will be better to implement it as a static class (note that I specified that you will not connect, ever to several databases or have several threads).
So you will not need to create several connection objects, because you already know that you will only use one. And you will not need to create several objects. Singletons in this scenario are, also, an option.
There are other examples.
If you create an class to convert values.
class Convert{
static std::string fromIntToString(int value);
}
This way you will not need to create the class convert every time you need to convert from integer to an string.
std::string value = Convert::fromIntToString(10).
If you haven't done that you would need to instantiate this class several times through your program.
I know that you can find several other examples. It is up to you and your scenario to decide when you are going to do that.
I'm often running into the same trail of thought when I'm creating private methods, which application is to modify (usually initialize) an existing variable in scope of the class.
I can't decide which of the following two methods I prefer.
Lets say we have a class Test with a field variable x. Let it be an integer. How do you usually modify / initialize x ?
a) Modifying the field directly
private void initX(){
// Do something to determine x. Here its very simple.
x = 60;
}
b) Using a return value
private int initX(){
// Do something to determine x. Here its very simple.
return 60;
}
And in the constructor:
public Test(){
// a)
initX();
// b)
x = initX();
}
I like that its clear in b) which variable we are dealing with. But on the other hand, a) seems sufficient most of the time - the function name implies perfectly well what we are doing!
Which one do you prefer and why?
Thank for your answers guys! I'll make this a community wiki as I realize that there is no correct answer to this.
I usually prefer b), only I pick a different name, like computeX() in this case. A few reasons for why:
if I declare computeX() as protected, there is a simple way for a subclass to influent how it works, yet x itself can remain a private field;
I like to declare fields final if that's what they are; in this case a) is not an option since initialization has to happen in compiler (this is Java-specific, but your examples all look Java as well).
That said, I don't have a strong preference between the two methods. For instance, if I need to initialize several related fields at once, I will usually pick option a). That, though, only if I cannot or don't want for some reason, to initialize directly in constructor.
For initialization I prefer constructor initialization if it's possible,
public Test():x(val){...}, or write initialization code in the constructor body. Constructor is the best place to initialize all the fields (actually, it is the purpose of constructor). I'd use private initX() approach only if initialization code for X is too long (just for readability) and call this function from constructor. private int initX() in my opinion has nothing to do with initialization(unless you implement lazy initialization,but in this case it should return &int or const &int) , it is an accessor.
I would prefer option b), because you can make it a const function in languages that support it.
With option a), there is a temptation for new, lazy or just time-stressed developers to start adding little extra tasks into the initX method, instead of creating a new one.
Also, in b), you can remove initX() from the class definition, so consumers of the object don't even have to know it's there. For example, in C++.
In the header:
class Test {
private: int X;
public: Test();
...
}
In the CPP file:
static int initX() { return 60; }
Test::Test() {
X = initX();
}
Removing the init functions from the header file simplifies the class for the people that have to use it.
Neither?
I prefer to initialize in the constructor and only extract out an initialization method if I need a lot of fields initialized and/or need the ability to re-initialize at another point in the life time of an instance (without going through a destruct/construct).
More importantly, what does 60 mean?
If it is a meaningful value, make it a const with a meaningful name: NUMBER_OF_XXXXX, MINUTES_PER_HOUR, FIVE_DOZEN_APPLES, SPEED_LIMIT, ... regardless of how and where you subsequently use it (constructor, init method or getter function).
Making it a named constant makes the value re-useable in and of itself. And using a const is much more "findable", especially for more ubiquitous values (like 1 or -1) then using the actual value.
Only when you want to tie this const value to a specific class would it make sense to me to create a class const or var, or - it the language does not support those - a getter class function.
Another reason to make it a (virtual) getter function would be if descendant classes need the ability to start with a different initial value.
Edit (in response to comments):
For initializations that involve complex calculations I would also extract out a method to do the calculation. The choice of making that method a procedure that directly modifies the field value (a) or a function that returns the value it should be given (b), would be driven by the question whether or not the calculation would be needed at other times than "just the constructor".
If only needed at initialization in the constructor, I would prefer method (a).
If the calculation needs to be done at other times as well, I would opt for method (b) as it also makes it possible to assign the outcome to some other field or local variable and so can be used by descendants or other users of the class without affecting the inner state of the instance.
Actually only a) method behaves as expected (by analyzing method name). Method b) should be named 'return60' in your example or 'getXValue' in some more complicated one.
Both options are correct in my opinion. It all depeneds what was your intention when certain design was choosen. If your method has to do initialization only I would prefer a) beacuse it is simplier. In case x value is also used for something else somewhere in logic using b) option might lead to more consistent code.
You should also always write method names clearly and make those names corresponding with actual logic. (in this case method b) has confusing name).
#Frederik, if you use option b) and you have a LOT of field variables, the constructor will become a quite unwieldy block of code. Sometimes you just can't help but have lots and lots of member variables in a class (example: it's a domain object and it's data comes straight from a very wide table in the database). The most pragmatic approach would be to modularize the code as you need to.
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.