Related
#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.
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.
I have an object called Parameters that gets tossed from method to method down and up the call tree, across package boundaries. It has about fifty state variables. Each method might use one or two variables to control its output.
I think this is a bad idea, beacuse I can't easily see what a method needs to function, or even what might happen if with a certain combination of parameters for module Y which is totally unrelated to my current module.
What are some good techniques for decreasing coupling to this god object, or ideally eliminating it ?
public void ExporterExcelParFonds(ParametresExecution parametres)
{
ApplicationExcel appExcel = null;
LogTool.Instance.ExceptionSoulevee = false;
bool inclureReferences = parametres.inclureReferences;
bool inclureBornes = parametres.inclureBornes;
DateTime dateDebut = parametres.date;
DateTime dateFin = parametres.dateFin;
try
{
LogTool.Instance.AfficherMessage(Variables.msg_GenerationRapportPortefeuilleReference);
bool fichiersPreparesAvecSucces = PreparerFichiers(parametres, Sections.exportExcelParFonds);
if (!fichiersPreparesAvecSucces)
{
parametres.afficherRapportApresGeneration = false;
LogTool.Instance.ExceptionSoulevee = true;
}
else
{
The caller would do :
PortefeuillesReference pr = new PortefeuillesReference();
pr.ExporterExcelParFonds(parametres);
First, at the risk of stating the obvious: pass the parameters which are used by the methods, rather than the god object.
This, however, might lead to some methods needing huge amounts of parameters because they call other methods, which call other methods in turn, etcetera. That was probably the inspiration for putting everything in a god object. I'll give a simplified example of such a method with too many parameters; you'll have to imagine that "too many" == 3 here :-)
public void PrintFilteredReport(
Data data, FilterCriteria criteria, ReportFormat format)
{
var filteredData = Filter(data, criteria);
PrintReport(filteredData, format);
}
So the question is, how can we reduce the amount of parameters without resorting to a god object? The answer is to get rid of procedural programming and make good use of object oriented design. Objects can use each other without needing to know the parameters that were used to initialize their collaborators:
// dataFilter service object only needs to know the criteria
var dataFilter = new DataFilter(criteria);
// report printer service object only needs to know the format
var reportPrinter = new ReportPrinter(format);
// filteredReportPrinter service object is initialized with a
// dataFilter and a reportPrinter service, but it doesn't need
// to know which parameters those are using to do their job
var filteredReportPrinter = new FilteredReportPrinter(dataFilter, reportPrinter);
Now the FilteredReportPrinter.Print method can be implemented with only one parameter:
public void Print(data)
{
var filteredData = this.dataFilter.Filter(data);
this.reportPrinter.Print(filteredData);
}
Incidentally, this sort of separation of concerns and dependency injection is good for more than just eliminating parameters. If you access collaborator objects through interfaces, then that makes your class
very flexible: you can set up FilteredReportPrinter with any filter/printer implementation you can imagine
very testable: you can pass in mock collaborators with canned responses and verify that they were used correctly in a unit test
If all your methods are using the same Parameters class then maybe it should be a member variable of a class with the relevant methods in it, then you can pass Parameters into the constructor of this class, assign it to a member variable and all your methods can use it with having to pass it as a parameter.
A good way to start refactoring this god class is by splitting it up into smaller pieces. Find groups of properties that are related and break them out into their own class.
You can then revisit the methods that depend on Parameters and see if you can replace it with one of the smaller classes you created.
Hard to give a good solution without some code samples and real world situations.
It sounds like you are not applying object-oriented (OO) principles in your design. Since you mention the word "object" I presume you are working within some sort of OO paradigm. I recommend you convert your "call tree" into objects that model the problem you are solving. A "god object" is definitely something to avoid. I think you may be missing something fundamental... If you post some code examples I may be able to answer in more detail.
Query each client for their required parameters and inject them?
Example: each "object" that requires "parameters" is a "Client". Each "Client" exposes an interface through which a "Configuration Agent" queries the Client for its required parameters. The Configuration Agent then "injects" the parameters (and only those required by a Client).
For the parameters that dictate behavior, one can instantiate an object that exhibits the configured behavior. Then client classes simply use the instantiated object - neither the client nor the service have to know what the value of the parameter is. For instance for a parameter that tells where to read data from, have the FlatFileReader, XMLFileReader and DatabaseReader all inherit the same base class (or implement the same interface). Instantiate one of them base on the value of the parameter, then clients of the reader class just ask for data to the instantiated reader object without knowing if the data come from a file or from the DB.
To start you can break your big ParametresExecution class into several classes, one per package, which only hold the parameters for the package.
Another direction could be to pass the ParametresExecution object at construction time. You won't have to pass it around at every function call.
(I am assuming this is within a Java or .NET environment) Convert the class into a singleton. Add a static method called "getInstance()" or something similar to call to get the name-value bundle (and stop "tramping" it around -- see Ch. 10 of "Code Complete" book).
Now the hard part. Presumably, this is within a web app or some other non batch/single-thread environment. So, to get access to the right instance when the object is not really a true singleton, you have to hide selection logic inside of the static accessor.
In java, you can set up a "thread local" reference, and initialize it when each request or sub-task starts. Then, code the accessor in terms of that thread-local. I don't know if something analogous exists in .NET, but you can always fake it with a Dictionary (Hash, Map) which uses the current thread instance as the key.
It's a start... (there's always decomposition of the blob itself, but I built a framework that has a very similar semi-global value-store within it)
I'm designing a language, and I'm wondering if it's reasonable to make reference types non-nullable by default, and use "?" for nullable value and reference types. Are there any problems with this? What would you do about this:
class Foo {
Bar? b;
Bar b2;
Foo() {
b.DoSomething(); //valid, but will cause exception
b2.DoSomething(); //?
}
}
My current language design philosophy is that nullability should be something a programmer is forced to ask for, not given by default on reference types (in this, I agree with Tony Hoare - Google for his recent QCon talk).
On this specific example, with the unnullable b2, it wouldn't even pass static checks: Conservative analysis cannot guarantee that b2 isn't NULL, so the program is not semantically meaningful.
My ethos is simple enough. References are an indirection handle to some resource, which we can traverse to obtain access to that resource. Nullable references are either an indirection handle to a resource, or a notification that the resource is not available, and one is never sure up front which semantics are being used. This gives either a multitude of checks up front (Is it null? No? Yay!), or the inevitable NPE (or equivalent). Most programming resources are, these days, not massively resource constrained or bound to some finite underlying model - null references are, simplistically, one of...
Laziness: "I'll just bung a null in here". Which frankly, I don't have too much sympathy with
Confusion: "I don't know what to put in here yet". Typically also a legacy of older languages, where you had to declare your resource names before you knew what your resources were.
Errors: "It went wrong, here's a NULL". Better error reporting mechanisms are thus essential in a language
A hole: "I know I'll have something soon, give me a placeholder". This has more merit, and we can think of ways to combat this.
Of course, solving each of the cases that NULL current caters for with a better linguistic choice is no small feat, and may add more confusion that it helps. We can always go to immutable resources, so NULL in it's only useful states (error, and hole) isn't much real use. Imperative technqiues are here to stay though, and I'm frankly glad - this makes the search for better solutions in this space worthwhile.
Having reference types be non-nullable by default is the only reasonable choice. We are plagued by languages and runtimes that have screwed this up; you should do the Right Thing.
This feature was in Spec#. They defaulted to nullable references and used ! to indicate non-nullables. This was because they wanted backward compatibility.
In my dream language (of which I'd probably be the only user!) I'd make the same choice as you, non-nullable by default.
I would also make it illegal to use the . operator on a nullable reference (or anything else that would dereference it). How would you use them? You'd have to convert them to non-nullables first. How would you do this? By testing them for null.
In Java and C#, the if statement can only accept a bool test expression. I'd extend it to accept the name of a nullable reference variable:
if (myObj)
{
// in this scope, myObj is non-nullable, so can be used
}
This special syntax would be unsurprising to C/C++ programmers. I'd prefer a special syntax like this to make it clear that we are doing a check that modifies the type of the name myObj within the truth-branch.
I'd add a further bit of sugar:
if (SomeMethodReturningANullable() into anotherObj)
{
// anotherObj is non-nullable, so can be used
}
This just gives the name anotherObj to the result of the expression on the left of the into, so it can be used in the scope where it is valid.
I'd do the same kind of thing for the ?: operator.
string message = GetMessage() into m ? m : "No message available";
Note that string message is non-nullable, but so are the two possible results of the test above, so the assignment is value.
And then maybe a bit of sugar for the presumably common case of substituting a value for null:
string message = GetMessage() or "No message available";
Obviously or would only be validly applied to a nullable type on the left side, and a non-nullable on the right side.
(I'd also have a built-in notion of ownership for instance fields; the compiler would generate the IDisposable.Dispose method automatically, and the ~Destructor syntax would be used to augment Dispose, exactly as in C++/CLI.)
Spec# had another syntactic extension related to non-nullables, due to the problem of ensuring that non-nullables had been initialized correctly during construction:
class SpecSharpExampleClass
{
private string! _nonNullableExampleField;
public SpecSharpExampleClass(string s)
: _nonNullableExampleField(s)
{
}
}
In other words, you have to initialize fields in the same way as you'd call other constructors with base or this - unless of course you initialize them directly next to the field declaration.
Have a look at the Elvis operator proposal for Java 7. This does something similar, in that it encapsulates a null check and method dispatch in one operator, with a specified return value if the object is null. Hence:
String s = mayBeNull?.toString() ?: "null";
checks if the String s is null, and returns the string "null" if so, and the value of the string if not. Food for thought, perhaps.
A couple of examples of similar features in other languages:
boost::optional (C++)
Maybe (Haskell)
There's also Nullable<T> (from C#) but that is not such a good example because of the different treatment of reference vs. value types.
In your example you could add a conditional message send operator, e.g.
b?->DoSomething();
To send a message to b only if it is non-null.
Have the nullability be a configuration setting, enforceable in the authors source code. That way, you will allow people who like nullable objects by default enjoy them in their source code, while allowing those who would like all their objects be non-nullable by default have exactly that. Additionally, provide keywords or other facility to explicitly mark which of your declarations of objects and types can be nullable and which cannot, with something like nullable and not-nullable, to override the global defaults.
For instance
/// "translation unit 1"
#set nullable
{ /// Scope of default override, making all declarations within the scope nullable implicitly
Bar bar; /// Can be null
non-null Foo foo; /// Overriden, cannot be null
nullable FooBar foobar; /// Overriden, can be null, even without the scope definition above
}
/// Same style for opposite
/// ...
/// Top-bottom, until reset by scoped-setting or simply reset to another value
#set nullable;
/// Nullable types implicitly
#clear nullable;
/// Can also use '#set nullable = false' or '#set not-nullable = true'. Ugly, but human mind is a very original, mhm, thing.
Many people argue that giving everyone what they want is impossible, but if you are designing a new language, try new things. Tony Hoare introduced the concept of null in 1965 because he could not resist (his own words), and we are paying for it ever since (also, his own words, the man is regretful of it). Point is, smart, experienced people make mistakes that cost the rest of us, don't take anyones advice on this page as if it were the only truth, including mine. Evaluate and think about it.
I've read many many rants on how it's us poor inexperienced programmers who really don't understand where to really use null and where not, showing us patterns and antipatterns that are meant to prevent shooting ourselves in the foot. All the while, millions of still inexperienced programmers produce more code in languages that allow null. I may be inexperienced, but I know which of my objects don't benefit from being nullable.
Here we are, 13 years later, and C# did it.
And, yes, this is the biggest improvement in languages since Barbara and Stephen invented types in 1974.:
Programming With Abstract Data Types
Barbara Liskov
Massachusetts Institute of Technology
Project MAC
Cambridge, Massachusetts
Stephen Zilles
Cambridge Systems Group
IBM Systems Development Division
Cambridge, Massachusetts
Abstract
The motivation
behind the work in very-high-level languages is to ease the
programming task by providing the programmer with a language
containing primitives or abstractions suitable to his problem area.
The programmer is then able to spend his effort in the right place; he
concentrates on solving his problem, and the resulting program will be
more reliable as a result. Clearly, this is a worthwhile goal.
Unfortunately, it is very difficult for a designer to select in
advance all the abstractions which the users of his language might
need. If a language is to be used at all, it is likely to be used to
solve problems which its designer did not envision, and for which the
abstractions embedded in the language are not sufficient. This paper
presents an approach which allows the set of built-in abstractions to
be augmented when the need for a new data abstraction is discovered.
This approach to the handling of abstraction is an outgrowth of work
on designing a language for structured programming. Relevant aspects
of this language are described, and examples of the use and
definitions of abstractions are given.
I think null values are good: They are a clear indication that you did something wrong. If you fail to initialize a reference somewhere, you'll get an immediate notice.
The alternative would be that values are sometimes initialized to a default value. Logical errors are then a lot more difficult to detect, unless you put detection logic in those default values. This would be the same as just getting a null pointer exception.
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.