In Red, there are functions of datatypes function!, op!, native!, routine! and action!. What are the differences between them? As far as I know function! is used for user-defined functions and op! for infix operators, and routine! for functions defined in Red/System, but why is there a need for the other two?
function!
As you've guessed yourself, function!s are user-defined functions that support refinements and typechecking, and can also contain embedded docstrings.
Typically, function! values are created with func, function, does and has constructors, and utilize so-called spec dialect; but, in theory, nothing stops you from making your own constructors or devising your own spec formats.
It's also worth noting that function!s fully support reflection.
op!
op!s are infix wrappers on top of other 4 types of functions - they take one value on the left and result of an expression on the right, and they also take precedence other functions during evaluation.
op! values are limited to two arguments, don't support refinements, and have a limited support for reflection (e.g. you can't inspect their bodies with body-of).
routine!
routines! exist in both realms of Red and Red/System (low-level dialect on top of which Red runtime is build). Their specs are written in spec dialect, but their bodies contain Red/System code. Oh, and they support reflection.
Usually they are used for library bindings (like the SQL lib you've mentioned), interaction with runtime, or for performance bottlenecks (Red/System is a compiled language, so rewriting perfomance-critial parts of your app as a set of routine!s will give you a significant boost, at the cost of mandatory compilation).
native!
native!s are functions written in Red/System (for perfomance, simplicity or feasibility reasons) and compiled down to native code (hence the name). Not sure what else can be said about them, aside from implementation details. native! aren't very user-facing, so you might want to study Red's source code in case you have any questions left.
action!
action!s are a standardized set of function written in Red/System (just like native!s) that each datatype implements (or inherits) as its "method". action! are polymorphic in a sense that they dispatch on their first argument:
>> add 1 2%
== 1.02
>> add 2% 1
== 102%
>> append [1] "2"
== [1 "2"]
>> append "1" [2]
== "12"
In mainstream languages this typically looks like "1".append([2]) or something like that.
Distinction between action!s and native!s boils down to a design choice:
you can have as many native! as you want, but action!s, for efficiency, have a fixed-size dispatch table (which means that maximum number of action!s per datatype is limited; minimum number is two: make [to create value] and mold [to serialize value to string!]).
logically, action!s are organized around datatype to which they belong, in one file, while native!s aren't really concerned with datatypes, and implement control flow, trigonometric functions, operations on sets, etc.
Coincidentially, just recently we have a similar discussion about action!s and native!s in our community chat, which you might want to read. I can also recommend to skim thru Rudolf Meijer's Red specification draft, and, of course, official reference documentation.
As for "why" in your question - distinction between 5 types is just an implementation detail, inherited from Rebol. Logically, they all implement what you might call a "function" from conceptual standpoint, and fall into any-function! camp.
While to a caller it may seem similar to run a function whose body is a BLOCK! of code to one which is implemented as native instructions...the implementation has to go down a different branch.
I don't know precisely what Red does in the compilation case, the interpreter case for Rebol2 and Red are similar. These different types are effectively part of a big switch() statement. If it looks in the cell describing the "function" and finds TYPE_NATIVE it knows to interpret the cell's contents as containing a native function pointer. If it finds TYPE_FUNCTION, it knows to pick apart the cell as containing a pointer to a block of code to execute:
https://github.com/red/red/blob/cb39b45f90585c8f6392dc4ccfc82ebaa2e312f7/runtime/interpreter.reds#L752
Now I myself would agree with your line of questioning. e.g. is this leaking an implementation detail to the user--who shouldn't be concerned with this facet in the type system?
But for what it is worth, there is a catch-all typeset called ANY-FUNCTION!:
>> any-function!
== make typeset! [native! action! op! function! routine!]
And you might think of that as "anything that obeys a function-like interface for calling". There are some complexities however, as OP! gets its first argument from the left...so that really is a matter of concern from an interface perspective.
Anyway... a NATIVE! (body is built as native code into the executable) vs. a FUNCTION! (body is a block of Red code run by interpretation or compilation) is just one distinction. A ROUTINE! is a facade built to interact with a DLL/library a la FFI that did not have a-priori knowledge of Red. An ACTION! is a very oversimplified attempt at what are called in other languages Generics. An OP! just gets its first argument from the left.
Point being that each of these might feel the same to a caller (except OP!), but the implementation has to do something different. The way it knows to do something different is via a type byte in a value cell. That's how Rebol2 did it--and Red followed Rebol2 fairly closely--so that's how it also does it. It means that any novel concept of what provides the implementation behind a function requires a new datatype, and it's probably not the greatest idea.
Red is based on Rebol an so has the same types.
function! is an user defined function defined in red
native! is an function in machinecode
op! is an infix operator written in machinecode
action! is an polymorphic function in machinecode
routine! is an function in imported from dynamic library
Related
Making subs/procedures available for reuse is one core function of modules, and I would argue that it is the fundamental way how a language can be composable and therefore efficient with programmer time:
if you create a type in your module, I can create my own module that adds a sub that operates on your type. I do not have to extend your module to do that.
# your module
class Foo {
has $.id;
has $.name;
}
# my module
sub foo-str(Foo:D $f) is export {
return "[{$f.id}-{$f.name}]"
}
# someone else using yours and mine together for profit
my $f = Foo.new(:id(1234), :name("brclge"));
say foo-str($f);
As seen in Overloading operators for a class this composability of modules works equally well for operators, which to me makes sense since operators are just some kinda syntactic sugar for subs anyway (in my head at least). Note that the definition of such an operator does not cause any surprising change of behavior of existing code, you need to import it into your code explicitly to get access to it, just like the sub above.
Given this, I find it very odd that we do not have a similar mechanism for methods, see e.g. the discussion at How do you add a method to an existing class in Perl 6?, especially since perl6 is such a method-happy language. If I want to extend the usage of an existing type, I would want to do that in the same style as the original module was written in. If there is a .is-prime on Int, it must be possible for me to add a .is-semi-prime as well, right?
I read the discussion at the link above, but don't quite buy the "action at a distance" argument: how is that different from me exporting another multi sub from a module? for example the rust way of making this a lexical change (Trait + impl ... for) seems quite hygienic to me, and would be very much in line with the operator approach above.
More interesting (to me at least) than the technicalities is the question if language design: isn't the ability to provide new verbs (subs, operators, methods) for existing nouns (types) a core design goal for a language like perl6? If it is, why would it treat methods differently? And if it does treat them differently for a good reason, does that not mean we are using way to many non-composable methods as nouns where we should be using subs instead?
From a language design perspective, it all comes down to a simple question: which language are we speaking? In Perl 6, this is a question about which we always try to be very clear.
The notion of ones current language in Perl 6 is defined entirely in terms of lexical scope. Sub declarations are lexically scoped. When we import symbols from a module, including extra multi candidates, those are lexically scoped. When we perform language tweaks - such as introducing new operators - those are lexically scoped. Verbs in our current language - that is, subroutine calls - are those with a lexical definition. (Operators are simply sub calls with more interesting parsing.) Since lexical scopes are closed at the end of compile time, the compiler has a complete view of the current language. That's why sub calls to non-existent subs, or references to undeclared variables, are detected and reported at compile time, as well as some basic compile-time type checking; future Perl 6 versions are likely to extend the set of compile-time checks that can be expected. The current language is the static, early-bound, part of Perl 6.
By contrast, a method call is a verb to be interpreted in the target object's language. This is the dynamic, late-bound, part of Perl 6. While the most immediate result of that is the typical polymorphism found in various forms in implementations of OO, thanks to meta-programming even the manner in which a verb is interpreted is up for grabs. For example, a monitor will acquire a lock while it interprets the verb and release it afterwards. Other objects might have been constructed based on things other than Perl 6 code, and so the interpretation of a verb doesn't mean invoking code written as a Perl 6 method. Or the code might be somewhere over the network. Who knows? Well, certainly not the caller, and that's the point, and the power, and the risk, of late binding.
The Perl 6 answer to "I want to extend the range of verbs I can use with this object in my current language" is very simple: use language features that relate to extending the current language! There's even a special syntax, $obj.&foo, that allows for a verb foo to be defined in the current language - by writing a sub - and then invoked much as if it's a method on the object. However, the small syntactic distinction makes it clear to the reader - and to the compiler - what is going on, and which language is getting to define that verb.
Through the use of augment it is possible to extend the language defined by some type of objects. However, it's rarely the best way to do things, given that it will have global effect, and also scatter the definition of the language of the object.
Much of what we do in programming is about building languages. By that I don't mean new syntax; most of our new languages - even in a language as open to mutation as Perl 6 - are just nouns and verbs defined using standard language features. However, in any non-trivial program, we can't keep every detail of every language in mind at once. When I go to the restaurant and order a schnitzel, I don't know how the order will be transported to the kitchen, what the kitchen looks like, whether the schnitzel is hammered out, breaded, and cooked on demand, or just served from a (hopefully not too stale) cache of prepared schnitzels. The kitchen and I have just enough shared meaning to make the right kind of thing happen, but I don't know how they'll precisely react to my request and they need not know what I'll do in the meantime. This kind of thinking is acknowledged by OO itself - at least when we fully embrace it - and at a larger scale by concepts such as bounded contexts, as found in Domain Driven Design.
In summary, Perl 6 tries to help us keep our languages straight: to know what is in our current language, and what we express with only limited understanding. That distinction is encoded by the sub/method distinction, which also turns out to be a sensible place to hang a static/dynamic distinction too.
I've started playing around with Kotlin, but I sense my own limitation in the way I program. My problem is that I still think Java therefore the style is still imperative, my question is to all functional programming zealots , which I believe would be very useful to all people who at the very beginning stage and also need to 'brake' their brain to start building it again; to leave comfort zone and start thinking pseudo and not in "whatever is your first language". I believe it is possible for highly experienced polyglot developers to chew the concepts down to plain advices of what makes your program being written in entirely functional way and what violates the paradigm. I don't know all the quirks but please don't hesitate to include universally accepted terms which might be unknown to me(I can always lookup). At this point I need this set of rules to make myself suffer at first and not break them but then I know I will feel it, analyze guidelines and understand how they are worse/better which of course is my own homework.
So example of these guidelines, would be something like:
Never change state, this can be avoided by using x, y, z
Operate using higher order functions only (I maybe wrong, just example)
I hope the answer will give me long term reference to put myself in extreme conditions where I stop escaping to OOP whenever I feel uncomfortable. And now when I look at Kotlin I understand how I've should've been thinking about problems, it is about intention not about the structure imposed by one language or another. Intention can always be converted to a language of your choice and backed up by design patterns applicable to the language, but to find that middle ground I need to jail myself first from the comfort zone.
Avoid mutable state like the plague.
One of the main points of using functional programming, possibly the main one, is to avoid all the little pitfalls, bugs, issues one needs to deal with when using mutable state. You should do everything you can in order to avoid mutating state. For instance, instead of using C-style for-loops where you need to keep a counter variable updated, use map and other higher-order functions in order to abstract away your iteration patterns. This also means that you should never change the value of a variable if you can avoid that. Instead, you should be defining almost all of your variables, preferrably all of them, as constants, and using functions to compute new values from them instead of mutating them.
Avoid side-effects like the plague.
Mutable state's ugly cousin, side-effects. Side effects mean anything other than taking a value and returning a value in a function. If that function prints data, mutates global variables, sends messages to threads, or anything, anything other than simply taking its parameters, computing a value from them, and returning a value, that function has side-effects. Side-effects are important (see next bullet point), but if you use them a lot, they get impossible to track. Just think of how everyone tells you to avoid global variables in imperative programming. Functional programming goes a step further and tries to avoid all side-effects. The bulk of your program should be made of pure functions. (See ahead)
When you need to use side-effects, keep them contained.
Yes, I just told you to run away from side-effects. However, no program is useful without side-effects of some kind. Graphical User Interface? Side-effect. Audio output? Side-effect. Printing to a shell? Side-effect. So you can't really get rid of side-effects if you want to build useful stuff.
What you should do instead is write your code so that all your side-effecting code lives in a thin layer which mostly calls pure functions and then does the required side-effects using the result of these pure function calls.
Use pure functions for everything you can.
This is sort of the flipside of the previous point. A pure function is a function which has no side-effects and does not mutate anything. It can only take in parameters and return a value. You should use these a lot. For instance, instead of doing your logging within functions which are computing stuff, you should be constructing your log strings using pure functions, and then letting your side-effects layer call these pure functions, call more pure functions in order to format the log strings into a full log, and then output the log itself from your side-effects layer.
Use higher-order functions to structure your code.
Higher-order functions are, in a way, the glue that makes functional programming work. A higher-order function is a function which takes one or more functions as parameters and/or returns a function. The power of higher-order functions is that they can encapsulate many of the patterns which you would use in an imperative-style program in a declarative manner. For instance, let's take a look at the three most common higher-order functions:
map is a function which takes a function and a list of values, applies its function argument to each of those values, and returns a new list with the results. map encapsulates the whole pattern of iterating over a list doing an operation on each value in a declarative manner.
filter is a function which takes a function which returns a boolean and a list of values, applies its function argument to each of those values and returns a list containing only those values for which its function argument returns true. It encapsulates the whole pattern of selecting results from a list in a declarative manner.
reduce, also known as fold, takes an initial value, a binary function and a list of values. It uses its function argument to combine the initial value with the first value of the list, then combines the result with the next value of the list and keeps on doing this until it has reduced the list to just one single value. It encapsulates the entire pattern of obtaining an aggregate value from a list of values.
This is in no way an exhaustive list of higher-order functions, but these three are the most common ones. I hope this has been enough to show how you can structure code which would require a lot of tracking variables using only functions in a declarative manner. If you use these higher-order functions well, it's likely you won't ever need a for or while loop again.
This is definitely not an exhaustive list of functional programming practices, but I think most functional programmers would agree these five guidelines form the core of what functional programming is about. If you want to really learn how to apply these, my advice would be to learn a pure functional programming language such as Haskell, so you are forced to abandon the imperative paradigm and to learn how to structure things functionally instead. I would recommend the fantastic Haskell Programming from First Principles as a starting resource if you choose to go this way. In case you don't want to/can't put down the cash, Brent Yorgey's Haskell course at UPenn is also a great free resource.
I'm studying lisp language (to do lisp routines) and in a general context i know what's a routine, but in a technical context i can talk about it, because i'm starting to learn routines now. So, what's the real definition of routine?
(i've already "googled" this but didn't find anything)
The term routine derives from subroutine, which is a more common term in languages like BASIC where one actually creates SUBroutines. (BASIC actually had a difference between a SUBroutine and a FUNCTION, but nevertheless...)
From the Wikipedia entry:
In computer science, a subroutine (also called procedure, function, routine, method, or subprogram) is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code.
As the name "subprogram" suggests, a subroutine behaves in much the same way as a computer program that is used as one step in a larger program or another subprogram. A subroutine is often coded so that it can be started ("called") several times and/or from several places during a single execution of the program, including from other subroutines, and then branch back (return) to the next instruction after the "call" once the subroutine's task is done.
Different languages/environments/eras have different ecosystems and thus different terms to describe the same general concept. I generally only use the term function (or method in an "OOP" environment) these days.
Happy coding.
For fun I have Community Wiki'ed. The list below is hopefully to cover which term(s) is (are) "correct" (widely accepted) to use in a given language to mean routine. Informally routine is used in context of all the languages below so it should be omitted unless it is the defacto term used. Feel free to add, correct, and annotate as appropriate.
C - function
Java - method. While function is also often used, the term function does not appear in the Java Language Specification.
C# - method and function. In the specification, functions refer to function-objects and anonymous functions. They are not the same as methods, which are members of types (classes or structures). Also consider delegates.
JavaScript - function or method. Methods are functions accessed via a property of an object.
Haskell - function. This is the accepted terminology.
Scala - function or method. Method if def member of type, functions are first-class values.
BASIC - function or subroutine. Subroutines do not return values. Supports call-by-reference.
FORTRAN - function or subroutine. Subroutines do not return values. Supports call-by-reference.
LISP - function. DEFUN -> DEfineFUNction, all forms are valid expressions. Also consider macros, which are not themselves functions but are arguably routines.
VHDL - subprograms: functions and procedures. Procedures have no return value.
SmallTalk - method
Python - method
Ruby - method (often interchanged with function? lambdas/Procs may be considered different?)
Perl - function and subroutine. There is only one form to declare a function/SUBroutine so there is no distinction w.r.t. return values. Using method (for object-bound functions) seems less prevalent than in other languages.
Pascal - procedures and functions
Ada - procedures and functions
You can't find a technical definition because there isn't a technical definition specific to lisp. A 'routine', outside of vaudeville, is just another name for a function. While it's been many years since I programmed in Lisp full-time, no one ever used that term in any formal way, or even used it commonly. We talked about 'functions', 'macros', and 'forms.' If someone said, 'oh, there's a routine to calculate how many apples in a pie' it was perfectly informal.
Java forbids operator overloading, but coming from C++ I do not see any reason for that. In languages where operator symbols are symbols as any other, same rules apply to "+" as to"plus" and there is no problem. So what is the point?
Edit: To be more concrete, show me which disadvantage overloaded "+" may have over overloaded "equals".
Just as many other things in Java, this is a restriction because it may be confusing if used improperly. (Similarly as pointer arithmetic is forbidden because it is error prone.) I'm a big fan of Java, but I'm generally of the opinion that it shouldn't be forbidden just because it could be misused.
For instance, BigInteger would benefit greatly from overloading the + operator.
OK, I'll try my hand at this under the assumption that Gabriel Ščerbák is doing this for better reasons than railing against a language.
The issue for me is one of manageable complexity: How much of the code in front of me do I have to decode vs. simply read?
In most conventional languages, upon seeing the expression a + b I know what is going to happen. The variables a and b will be added together. I'm pretty confident that behind the scenes the code will be very concise, very fast native machine code that adds the two numbers, whether the numbers are short integers or double-precision or some mixture of the two. (In some languages I may have to also assume that these could be strings being concatenated, but that's a rant for an entirely different question -- but one that flavours this rant if you peer at it from the right angle.)
When I make my own user-defined type -- say the omnipresent Complex type (and why Complex isn't a standard data type in modern languages is way the Hell beyond me, but that, again, is a rant for a different question) -- if I overload an operator (or, rather, if the operator is overloaded for me -- I'm using a library, say), short of peering very closely at the code I will not know that I'm now calling (possibly-virtual) methods on objects instead of having very tight, concise code generated for me behind the scenes. I will not know of the hidden conversions, the hidden temporary variables, the ... well, everything that goes along with writing many operators. To find out what's really going on in my code I have to pay very close attention to every line and keep track of declarations that may be three screens away from my current location in the code. To say that this impedes my understanding of the code flowing before my eyes is an understatement. Important details are being lost because the syntactic sugar is making things taste too tasty.
When I'm forced to use explicit methods on the objects (or even static methods or global methods where that applies) this is a signal to me, while I'm reading, that tells me of the potential cost overheads and bottlenecks and the like. I know, without even having to think for an instant, that I'm dealing with a method, that I've got dispatching overhead, that I may have temporary object creation and deletion overhead, etc. Everything's in front of me right before my eyes -- or at least enough indicators are in front of me that I know to be more careful.
I'm not intrinsically opposed to operator overloading. There are times when it makes code clearer, yes indeed, especially when you have complicated calculations over many baffling expressions. I can understand, however, exactly why someone might not want to put that into their language.
There is a further reason not to like operator overloading from the language designer's viewpoint. Operator overloading makes for very, very, very difficult grammars. C++ is already infamous for being nigh-unparseable and some of its constructs, like operator overloading, are the cause of it. Again from the viewpoint of someone writing the language I can fully understand why operator overloading was left off as a bad idea (or a good idea that's bad in implementation).
(This is all, of course, in addition to the other reasons you've already rejected. I'll submit my own overloading of operator-,() in my old C++ days in that stew just to be really annoying.)
There is no problem with operator overloading itself, but how it's actually has been used. As long as you overload the operators to make sense, the language still makes sense, but if you give other meanings to operators, it makes the language inconsistent.
(One example is how the shift left (<<) and shift right (>>) operators has been overloaded in C++ to mean "input" and "output"...)
So, the reasoning when leaving out operator overloading was probably that the risk of misuse was greater than the benefits of having operator overloading.
I think that Java would benefit greatly from extending its operators to cover built-in Number object types. Early (pre-1.0) versions of Java were said to have it (in that there were no primitives - everything was an object) but the VM technology of the time made it prohibitive from a performance view.
But in terms of in general allowing user defined operator overloading, it is not in the spirit of the Java language. The main problem is simply that it is hard to implement an operator that is consistent with what you expect from mathematics across object types and it will open the door to a lot of bad implementations which lead to a lot of hard to find (therefore expensive) bugs. You can just look at how many bad equals implementations (as in violate the contract) there are in general Java code, and the problem would only get worse from there.
Of course there are languages that prioritize power and syntactical beauty over such concerns, and more power to them. It is just not Java.
Edit: How is a custom + operator different than a custom == implementation (captured in Java in the equals(Object) method)? It isn't, really. It is just that by allowing operator overloading, things that are intuitive to a sixth grader become untrue. The real world experience of equals(Object) implementations shows how such complex contracts become hard to enforce in the real world.
Further Edit: Let me clarify the above, as I shortened it while editing and lost the point. A + operator in math has certain properties, one of which is that it doesn't matter which order the numbers on either side appear - it has the same result. So consider even the simplest case of a + performing an add to a Collection:
Collection a = ...
Collection b = ...
a + b;
System.out.println(a);
System.out.println(b);
The intuitive understanding of + would lead to an expectation that a + b or b + a would give the same result, but of course they would not. Start mixing two object types that take each other as paramaters in their plus method (say Collection and String) and things get harder to follow.
Now certainly it is possible to design operators on objects which are well understood and lead to better, more readable and more understandable code than without them. But the point is that more often than not in home-grown corporate APIs what you would end up seeing is obfuscated code.
There are a few problems:
Overloading logical operators has side effects because of lazy evaluation.
Even in mathematical types there are ambiguities, is (3dpoint*3dpoint) a cross or scaler product
You can't define new operators, so people reuse existing operators in novel ways eg. "string1%string2" to mean split string1 on string2.
But you can't always protect idiots from themselves even with an outright ban.
The point is that whenever you see, for example, a plus sign being used in the code, you know exactly what it does given that you know the types of its operands (which you always do in Java, as it is strongly typed).
Apart from unambiguous clarity, why should we stick to:
car.getSpeed() and car.setSpeed(55)
when this could be used as well :
car.speed() and car.speed(55)
I know that get() and set() are useful to keep any changes to the data member manageable by keeping everything in one place.
Also, obviously, I understand that car.speed() and car.speed(55) are the same function, which makes this wrong, but then in PHP and also in Zend Framework, the same action is used for GET, POST, postbacks.
In VB and C# there are "properties", and are used by many, much to the disgust of purists I've heard, and there are things in Ruby like 5.times and .each, .to_i etc.
And you have operator overloading, multiple inheritance, virtual functions in C++, certain combinations of which could drive anyone nuts.
I mean to say that there are so many paradigms and ways in which things are done that it seems odd that nobody has tried the particular combination that I mentioned.
As for me, my reason is that it is short and cleaner to read the code.
Am I very wrong, slightly wrong, is this just odd and so not used, or what else?
If I still decide to stay correct, I could use car.speed() and car.setSpeed(55).
Is that wrong in any way (just omitting the "get" )?
Thanks for any explanations.
If I called car.speed(), I might think I am telling the car to speed, in other words to increase speed and break the speed limit. It is not clearly a getter.
Some languages allow you to declare const objects, and then restrict you to only calling functions that do not modify the data of the object. So it is necessary to have seperate functions for modification and read operations. While you could use overloads on paramaters to have two functions, I think it would be confusing.
Also, when you say it is clearer to read, I can argue that I have to do a look ahead to understand how to read it:
car.speed()
I read "car speed..." and then I see there is no number so I revise and think "get car speed".
car.getSpeed()
I read "for this car, get speed"
car.setSpeed(55)
I read "for this car, set speed to 55"
It seems you have basically cited other features of the language as being confusing, and then used that as a defense for making getters/setters more confusing? It almost sounds like are admitting that what you have proposed is more confusing. These features are sometimes confusing because of how general purpose they are. Sometimes abstractions can be more confusing, but in the end they often serve the purpose of being more reusable. I think if you wanted to argue in favor of speed() and speed(55), you'd want to show how that can enable new possibilities for the programmer.
On the other hand, C# does have something like what you describe, since properties behave differently as a getter or setter depending on the context in what they are used:
Console.WriteLine(car.Speed); //getter
car.Speed = 55 //setter
But while it is a single property, there are two seperate sections of code for implementing the getting and setting, and it is clear that this is a getter/setter and not a function speed, because they omit the () for properties. So car.speed() is clearly a function, and car.speed is clearly a property getter.
IMHO the C# style of having properties as syntatic sugar for get and set methods is the most expressive.
I prefer active objects which encapsulate operations rather than getters and setters, so you get a semantically richer objects.
For example, although an ADT rather than a business object, even the vector in C++ has paired functions:
size_type capacity() const // how many elements space is reserved for in the vector
void reserve(size_type n) // ensure space is reserved for at least n elements
and
void push_back ( const T& ) // inserts an element at the end
size_type size () const // the number of elements in the vector
If you drive a car, you can set the accelerator, clutch, brakes and gear selection, but you don't set the speed. You can read the speed off the speedometer. It's relatively rare to want both a setter and a getter on an object with behaviour.
FYI, Objective-C uses car.speed() and car.setSpeed(55) (except in a different syntax, [car speed] and [car setSpeed:55].
It's all about convention.
There is no right answer, it's a matter of style, and ultimately it does not matter. Spend your brain cycles elsewhere.
FWIW I prefer the class.noun() for the getter, and class.verb() for the setter. Sometimes the verb is just setNoun(), but other times not. It depends on the noun. For example:
my_vector.size()
returns the size, and
my_vector.resize(some_size)
changes the size.
The groovy approach to properties is quite excellent IMHO, http://groovy.codehaus.org/Groovy+Beans
The final benchmarks of your code should be this:
Does it work correctly?
Is it easy to fix if it breaks?
Is it easy to add new features in the future?
Is it easy for someone else to come in and fix/enhance it?
If those 4 points are covered, I can't imagine why anybody would have a problem with it. Most of the "Best Practices" are generally geared towards achieving those 4 points.
Use whichever style works for you, just be consistent about it, and you should be fine.
This is just a matter of convention. In Smalltalk, it's done the way you suggest and I don't recall ever hearing anybody complain about it. Getting the car's speed is car speed, and setting the car's speed to 55 is car speed:55.
If I were to venture a guess, I would say the reason this style didn't catch on is because of the two lines down which object-oriented programming have come to us: C++ and Objective-C. In C++ (even more so early in its history), methods are very closely related to C functions, and C functions are conventionally named along the lines of setWhatever() and do not have overloading for different numbers of arguments, so that general style of naming was kept. Objective-C was largely preserved by NeXT (which later became Apple), and NeXT tended to favor verbosity in their APIs and especially to distinguish between different kinds of methods — if you're doing anything but just accessing a property, NeXT wanted a verb to make it clear. So that became the convention in Cocoa, which is the de facto standard library for Objective-C these days.
It's convention Java has a convention of getters and setters C# has properties, python has public fields and JavaScript frameworks tend to use field() to get and field(value) to set
Apart from unambiguous clarity, why should we stick to:
car.getSpeed() and car.setSpeed(55)
when this could be used as well : car.speed() and car.speed(55)
Because in all languages I've encountered, car.speed() and car.speed(55) are the same in terms of syntax. Just looking at them like that, both could return a value, which isn't true for the latter if it was meant to be a setter.
What if you intend to call the setter but forget to put in the argument? The code is valid, so the compiler doesn't complain, and it doesn't throw an immediate runtime error; it's a silent bug.
.() means it's a verb.
no () means it's a noun.
car.Speed = 50;
x = car.Speed
car.Speed.set(30)
car.setProperty("Speed",30)
but
car.Speed()
implies command to exceed speed limit.