Recently I have been learning to program in Erlang as a long time C and C# developer. I am fairly new to functional programming. Now, I am trying to understand how do objects in languages like Scala work. I have been taught that OOP is all about changing state of given object using its public methods. Those methods change state of public properties and private members. But now I hear that in functional programming all objects should be immutable. Well, I agree that once assigned variable (in given function) should remain pointing to the same object. But does this "immutability" mean that I cannot change the internals (properties, private members) of given objects using their public methods? This makes objects just like simple data containers. It extracts all of the functionality outside of them. This makes objects act more like structures in C. It is something that is strange to me. Maybe I am missing something? Is it possible to use objects the old-fashioned-way and still consider it as functional programming?
You are mixing up three different concepts. Functional programming, mutability, and OOP are three different things.
I have been taught that OOP is all about changing state of given object using its public methods.
Yes and no. The important thing in OOP is that you have objects, which can simultaneously carry around data and code (their member methods), and that you talk to the objects using their interface, so that the object can then
dispatch to the concrete implementation of the called method
supply additional information that is stored in the data that the object carries (accessing this in the method implementation)
execute the code of the method implementation
Nobody prescribes you what this method call does, or that it must modify some state.
It happens to be that OOP helps to restore some basic sanity when working with state. This is because the horrifyingly complex global state of the application can be cut up into smaller pieces and hidden inside mutable objects. Moreover, those mutable objects can additionally attempt to maintain at least some local invariants, by prohibiting direct access to their state, and providing only a restricted set of operations that can modify that state.
But now I hear that in functional programming all objects should be immutable.
They should respect referential transparency. If your objects have no mutable state and only methods without any side effects, then it is sufficient for referential transparency. Sufficient, but not necessary: the objects can have more complex inner structure, but appear completely immutable from the outside. Caching is a good example.
Furthermore, even pure functional programs are not restricted to working with immutable data structures only. There is such thing as pure mutable state. The idea is that your functional programs are used to construct something like complex action plans for dealing with mutable state. The plan itself is an immutable entity. This plan can be very complex, but thanks to the fact that it is built from pure functions, it can be still sufficiently easy to reason about. This plan, which is built using only pure functions, can then be given to a small and simple interpreter, which executes the plan on mutable memory. In this way, you reap the benefits of both worlds: you have conceptual simplicity of pure functions while you are building the plan, but you also have the performance of close-to-the-metal computations when you execute this plan on mutable data structures.
But does this "immutability" mean that I cannot change the internals (properties, private members) of given objects using their public methods?
In general, yes. However, in Scala, immutability is not enforced by default. You can decide what parts of your application are complicated enough to reason about, so that it might be worth it to restrict yourself to pure functions. Everything else can be implemented using ordinary mutable structures, if this is easier.
This makes objects just like simple data containers. It extracts all of the functionality outside of them.
No, because objects still carry their virtual dispatch table with them. You can then ask the object from the outside to invoke the method apply(integer i), and the object, depending on what kind of object it is, might then invoke completely different things, like
/** get i-th character */
String.apply(integer i)
or
/** get value for key `i` */
TreeMap.apply(integer i)
You cannot do this with C structs without essentially re-implementing subclass polymorphism as a design pattern.
Is it possible to use objects the old-fashioned-way and still consider it as functional programming?
It's not an all-or-nothing game. You can start with a classical oop-language (with mutable state and all that), which supports the functional programming paradigm to some degree. You can then look at your application, and isolate those aspects of it that require more precise control over the side effects. You have to decide which side effects matter, and which are less critical. Then you can express the really critical parts using the somewhat stricter approach with pure functions (pure in the sense: as pure as you need them to be, i.e. not performing any critical side-effects without declaring it explicitly in their signature). The result would be a mix of classical OOP and FP in one application.
Writing programs using pure functions can be thought of as a construction of a proof in a somewhat primitive logic. It's nice if you can do it when you need it (using a stricter approach with pure functions), but it can also be nice if you can omit it when you don't need it (using the usual approach with messy side-effecty functions).
OOP is all about changing state of given object using its public methods.
It's a lie!
in functional programming all objects should be immutable
It's a lie!
But does this "immutability" mean that I cannot change the internals (properties, private members) of given objects using their public methods?
There are strict immutability and "simulated" immutability. With "simulated" immutability you can change internals, but you shouldn't produce visible changes. For example, caching of heavy computations is still acceptable.
Is it possible to use objects the old-fashioned-way and still consider it as functional programming?
It depends on how exactly you are mutating objects and how you define FP. Actually, god damn it, you can mutate objects in FP.
Maybe I am missing something?
Yes, there a lot of things you should learn.
There are several things you don't understand about immutable objects:
Immutable object still can has computed properties. So it's more than structure in C. See Uniform access principle for details. Note: in C# structure can have computed properties
Immutable object still can have useful methods. So it's more than structure in C. You can have some logic in immutable object, but this logic can't mutate state. Note: in C# structure can have computed properties.
Also, there is a huge difference between objects and structures in memory-safe languages (like C#, Scala, Erlang): you can't work easily with structures. Generally, there are no pointers in safe code (except things like unsafe regions). So you can't just share same structure between different structures.
Immutable object still can encapsulate some data. Encapsulation is the key to make abstractions (either good or bad)
Here are things that you should know about OOP:
OOP doesn't requires to mutate state. OOP without mutations is still OOP.
OOP has nice useful thing: inheritance. There are no such thing in pure FP.
Here are things that you should know about FP:
FP doesn't requires you to use immutable data. But it's much easier to work with immutable data in FP.
If a tree falls in the woods, does it make a sound?
If a pure function mutates some local data in order to produce an immutable return value, is that ok?"
Good FP languages have a lot of ways to work with mutable data to meet performance needs. FP just loves to hide mutations.
Only pure-FP languages are forcing you to use immutable data.
FP has get it's name for functions as first-class citizens. See more on wiki. You can use & pass functions just like you use & pass objects.
Well, a lot of FP is not about functions.
You should also know how OOP and FP are related:
Encapsulation and polymorphism works differently in OOP and FP. It's very clear how encapsulation work in OOP: private/protected and another access modifiers. But in pure FP only way to encapsulate some data is to use closures.
Polymorphism works differently in OOP and FP. In OOP you are using subtype polymorphism. But in pure FP you should use thing like protocols (interfaces) or multimethods.
“Closures are poor man's objects and vice versa”. You can express same code with closures and with objects.
C# and Scala are multi-paradigm languages. They both supports OOP and FP. It's not bad to mix OOP and FP. Actually it's best way to produce readable code.
And now, I want to explain why there a lot of people whom thinks that some paradigms can't be combined:
OOP was born before immutability become useful. In old days programs was simpler & we worried a lot about memory.
OOP was born before our CPU become able to parallel code. So, immutability (which makes writing parallel code easier) wasn't helpful.
Before recent popularity of FP it was useful primarily only for academists. Academists aren't in love with uncontrolled mutations.
Potentially FP program can be reorganized in such crazy ways that we can't depend on time order of side-effects (and mutations as part of side-effects). No time ordering = useless mutations. But languages like C#, Scala aren't so much crazy. But see next point.
FP has lazy computations at nearly birth. Also they have monads or similar mechanism to replace direct control flow. And function can be executed at any moment, because it's can be stored anywhere. And this make side-effects (and mutations) a bit harder for controlling.
Just to make things clear: creators of FP-style aren't idiots. They want side-effects to be explicit & controlled. So there is a nice concept: pure function.
Summary:
OOP is oftenly used with mutations. But it's not required. OOP is focused on objects.
FP is oftenly used with immutability. But it's not required. FP is focused on functions.
You can mix OOP, FP, mutations and immutability - all of them.
But does this "immutability" mean that I cannot change the internals
(properties, private members) of given objects using their public
methods?
Yes.
This makes objects just like simple data containers. It extracts all
of the functionality outside of them.
No. Typically much of the functionality of immutable classes is provided by their constructors. A constructor is not neccessarily just assigning values passed to it as arguments to member variables. Another part of the functionality can be found in getter-like methods that not only return the values of member variables but perform more complex transformations on them.
This makes objects act more like structures in C.
No. Structs in C are completely mutable. Anyone can access and modify their elements.
Related
I was reading some entries in Eric Lippert's blog about immutable data structures and I got to thinking, why doesn't C# have this built into the standard libraries? It seems strange for something with obvious reuse to not be already implemented out of the box.
EDIT: I feel I might be misunderstood on my question. I'm not asking how to implement one in C#, I'm asking why some of the basic data structures (Stack, Queue, etc.) aren't already available as immutable variants.
It does now.
.NET just shipped their first immutable collections, which I suggest you try out.
Any framework, language, or combination thereof that is not a purely experimental exercise has a market. Some purely experimental ones go on to develop a market.
In this sense, "market" does not necessarily refer to market economics, it's as true whether the producers of the framework/language/both are commercially or non-commercially oriented and distributing the framework/language/both (I'm just going to say "framework" for now on) at a cost or for free. Indeed, free-as-in-both-beer-and-speech projects can be even more heavily dependent on their markets than commercial projects in this way, because their producers are a subset of their market. The market is anyone and everyone who uses it.
The nature of this market will affect the framework in several ways both by organic processes (some parts prove more popular than others and get a bigger share of the mindspace within the community that educates its own members about them) and by fiat (someone decides a feature will serve the market and therefore adds it).
When .NET was developed, it was developed to serve its future market. Ideas about what would serve them therefore influenced decisions as to what should and should not be included in the FCL, the runtime, and the languages that work with it.
Someone decided that we'd quite likely need System.Collections.ArrayList. Someone decided we'd quite likely need System.IO.DirectoryInfo to have a Delete() method. Nobody decided we'd be likely to need a System.Collections.ImmutableStack.
Maybe nobody thought of it at all. Maybe someone did and even implemented it and then it was decided not to be of enough general use. Maybe it was debated at length within Microsoft. I've never worked for MS, so I don't have a clue.
What I can consider though, is the question as to what the people who were using the .NET framework in 2002 using in 2001.
Well, COM, ActiveX, ("Classic") ASP, and VB6 & VBScript is now much less used than it was, so it can be said to have been replaced by .NET. Indeed, that could be said to have been an intention.
As well as VB6 & VBScript, a considerable number who were writing in C++ and Java with Windows as a sole or primary target platform are now at least partly using .NET instead. Again, I think that could be said to be an intention, or at the very least I don't think MS were surprised that it went that way.
In COM we had an enumerator-object based foreach approach to iteration that had direct support in some languages (the VB family*), and .NET we have an enumerator-object based foreach approach to iteration that has direct support in some languages (C#, VB.NET, and others)†.
In C++ we had a rich set of collection types from the STL, and in .NET we have a rich set of collection types from the FCL (and typesafe generic types from .NET2.0 on).
In Java we had a strong everything-is-an-object style of OOP with a small set of methods provided by a common base-type and a boxing mechanism to allow for simple efficient primitives while keeping to this style. In .NET we have a strong everything-is-an-object style of OOP with a small set of methods provided by a common base-type and a (different) boxing mechanism to allow for simple efficient primitives while keeping to this style.
These cases show choices that are unsurprising considering who was likely to end up being the market for .NET (though such broad statements above shouldn't be read in a way that underestimates the amount of work and subtlety of issues within each of them). Another thing that relates to this is when .NET differs from COM or classic VB or C++ or Java, there may well be a bit of an explanation given in the documentation. When .NET differs from Haskell or Lisp, nobody feels the need to point it out!
Now, of course there are things done differently in .NET than to any of the above (or there'd have been no point and we could have stayed with COM etc.)
However, my point is that out of the near-infinite range of possible things that could end up in a framework like .NET, there are some complete no-brainers ("they might need some sort of string type..."), some close-to-obvious ("this is really easy to do in COM, so it must be easy to do in .NET"), some harder calls ("this will be more complicated than in VB6, but the benefits are worth it"), some improvements ("locale support could really be made a lot easier for developers, so lets build a new approach to the old issue") and some that were less related to the above.
At the other extreme, we can probably all imagine something that would be so out there as to be bizarre ("hey, all coders like Conway's Life - let's put a Conway's Life right into the framework") and hence there's no surprise at not finding it supported.
So far I've quickly brushed over a lot of hard work and difficult design balances in a way that makes the design they came up with seem simpler than it no doubt was. Most likely, the more "obvious" it seems to an outsider after the fact, the more difficult it was for the designers.
Immutable collection types falls into the large range of possible components to the FCL that while not as bizarre as a built-in-conway-support idea, was not as strongly called for by examining the market as a mutable list or a way to encapsulate locale information nicely. It would have been novel to much of the initial market, and therefore at risk of ending up not being used. In an alternate universe there's a .NET1.0 with immutable collections, but it's not very surprising that there wasn't one here.
*At least for consuming. Producing IEnumVARIANT implementations in VB6 wasn't simple, and could involve writing pointer values straight into v-tables in a rather nasty way that it suddenly occurs to me, is possibly not even allowed by today's DEP.
†With a sometimes impossible to implement .Reset() method. Is there any reason for this other than it was in IEnumVARIANT? Was it even ever much used in IEnumVARIANT?
I'll quote from that Eric Lippert blog that you've been reading:
because no one ever designed, specified, implemented, tested, documented and shipped that feature.
In other words, there is no reason other than it hasn't been high enough value or priority to get done ahead of all the other things they're working on.
Why can't you make an immutable struct? Consider the following:
public struct Coordinate
{
public int X
{
get { return _x; }
}
private int _x;
public int Y
{
get { return _y; }
}
private int _y;
public Coordinate(int x, int y)
{
_x = x;
_y = y;
}
}
It's an immutable value type.
It's hard to work with immutable data structures unless you have some functional programming constructs. Suppose you wanted to create an immutable vector containing every other capital letter. How would you do it unless you
A) had functions that did things like range(65, 91), filter(only even) and map(int -> char) to create the sequence in one shot and then turn it into an array
B) created the vector as mutable, added the characters in a loop, then then "froze" it, making it immutable?
By the way, C# does have the B option to some extent -- ReadOnlyCollection can wrap a mutable collection and prevent people from mutating it. However, it's a pain in the ass to do that all the time (and obviously it's hard to support sharing structure between copies when you don't know if something is going to become immutable or not.) A is a better option.
Remember, when C# 1.0 existed, it didn't have anonymous functions, it didn't have language support for generators or other laziness, it didn't have any functional APIs like LINQ -- not even map or filter -- it didn't have concise array initialization syntax (you couldn't write new int[] { 1, 2, 5 }) and it didn't have generic types; just putting stuff into and getting stuff out of collections normally was a pain. So I don't think it would have been a great choice to spend time on making robust immutable collections with such poor language support for using them.
It would be nice if .net had some really solid support for immutable data holders (classes and structures). One difficulty with adding really good support for such things, though, is that taking maximum advantage of mutable and immutable data structures would require some fundamental changes to the way inheritance works. While I would like to see such support in the next major object-oriented framework, I don't know that it can be efficiently worked into existing frameworks like .net or Java.
To see the problem, imagine that there are two basic data types: basicItem and deluxeItem (which is a basicItem with a few extra fields added). Each can exist in two concrete forms: mutable and immutable. Each can also be described in an abstract form: readable. Thus, there should be six data types; all but ReadableBasicItem should be substitutable for at least one other:
ReadableBasicItem: Not substitutable for anything
MutableBasicItem: ReadableBasicItem
ImmutableBasicItem: ReadableBasicItem
ReadableDeluxeItem: ReadableBasicItem
MutableDeluxeItem: ReadableDeluxeItem, MutableBasicItem (also ReadableBasicItem)
ImmutableDeluxeItem: ReadableDeluxeItem, ImmutableBasicItem (also ReadableBasicItem)
Even thought the underlying data type has just one base and one derived type, there inheritance graph has two "diamonds" since both "MutableDeluxeItem" and "ImmutableDeluxeItem" have two parents (MutableBasicItem and ReadableDeluxeItem), both of which inherit from ReadableBasicItem. Existing class architectures cannot effectively deal with that. Note that it wouldn't be necessary to support generalized multiple inheritance; merely to allow some specific variants such as those above (which, despite having "diamonds" in the inheritance graph, have an internal structure such that both ReadableDeluxeItem and MutableBasicItem would inherit from "the same" ReadableBasicItem).
Also, while support for that style of inheritance of mutable and immutable types might be nice, the biggest payoff wouldn't happen unless the system had a means of distinguishing heap-stored objects that should expose value semantics from those which should expose reference semantics, could distinguish mutable objects from immutable ones, and could allow objects to start out in an "uncommitted" state (neither mutable nor guaranteed immutable). Copying a reference to a heap object with mutable value semantics should perform a memberwise clone on that object and any nested objects with mutable value semantics, except in cases where the original reference would be guaranteed destroyed; the clones should start life as uncommitted, but be CompareExchange'd to mutable or immutable as needed.
Adding framework support for such features would allow copy-on-write value semantics to be implemented much more efficiently than would be possible without framework support, but such support would really have to be built into the framework from the ground up. I don't think it could very well be overlaid onto an existing framework.
I'm pretty new to C# so bear with me.
One of the first things I noticed about C# is that many of the classes are static method heavy. For example...
Why is it:
Array.ForEach(arr, proc)
instead of:
arr.ForEach(proc)
And why is it:
Array.Sort(arr)
instead of:
arr.Sort()
Feel free to point me to some FAQ on the net. If a detailed answer is in some book somewhere, I'd welcome a pointer to that as well. I'm looking for the definitive answer on this, but your speculation is welcome.
Because those are utility classes. The class construction is just a way to group them together, considering there are no free functions in C#.
Assuming this answer is correct, instance methods require additional space in a "method table." Making array methods static may have been an early space-saving decision.
This, along with avoiding the this pointer check that Amitd references, could provide significant performance gains for something as ubiquitous as arrays.
Also see this rule from FXCOP
CA1822: Mark members as static
Rule Description
Members that do not access instance data or call instance methods can
be marked as static (Shared in Visual Basic). After you mark the
methods as static, the compiler will emit nonvirtual call sites to
these members. Emitting nonvirtual call sites will prevent a check at
runtime for each call that makes sure that the current object pointer
is non-null. This can achieve a measurable performance gain for
performance-sensitive code. In some cases, the failure to access the
current object instance represents a correctness issue.
Perceived functionality.
"Utility" functions are unlike much of the functionality OO is meant to target.
Think about the case with collections, I/O, math and just about all utility.
With OO you generally model your domain. None of those things really fit in your domain--it's not like you are coding and go "Oh, we need to order a new hashtable, ours is getting full". Utility stuff often just doesn't fit.
We get pretty close, but it's still not very OO to pass around collections (where is your business logic? where do you put the methods that manipulate your collection and that other little piece or two of data you are always passing around with it?)
Same with numbers and math. It's kind of tough to have Integer.sqrt() and Long.sqrt() and Float.sqrt()--it just doesn't make sense, nor does "new Math().sqrt()". There are a lot of areas it just doesn't model well. If you are looking for mathematical modeling then OO may not be your best bet. (I made a pretty complete "Complex" and "Matrix" class in Java and made them fairly OO, but making them really taught me some of the limits of OO and Java--I ended up "Using" the classes from Groovy mostly)
I've never seen anything anywhere NEAR as good as OO for modeling your business logic, being able to demonstrate the connections between code and managing your relationship between data and code though.
So we fall back on a different model when it makes more sense to do so.
The classic motivations against static:
Hard to test
Not thread-safe
Increases code size in memory
1) C# has several tools available that make testing static methods relatively easy. A comparison of C# mocking tools, some of which support static mocking: https://stackoverflow.com/questions/64242/rhino-mocks-typemock-moq-or-nmock-which-one-do-you-use-and-why
2) There are well-known, performant ways to do static object creation/logic without losing thread safety in C#. For example implementing the Singleton pattern with a static class in C# (you can jump to the fifth method if the inadequate options bore you): http://www.yoda.arachsys.com/csharp/singleton.html
3) As #K-ballo mentions, every method contributes to code size in memory in C#, rather than instance methods getting special treatment.
That said, the 2 specific examples you pointed out are just a problem of legacy code support for the static Array class before generics and some other code sugar was introduced back in C# 1.0 days, as #Inerdia said. I tried to answer assuming you had more code you were referring to, possibly including outside libraries.
The Array class isn't generic and can't be made fully generic because this would break backwards compatibility. There's some sort of magic going on where arrays implement IList<T>, but that's only for single-dimension arrays with a lower bound of 0 – "list-ish" arrays.
I'm guessing the static methods are the only way to add generic methods that work over any shape of array regardless of whether it qualifies for the above-mentioned compiler magic.
I know this has been discussed many times, but I am not sure I really understand why Java and C# designers chose to omit this feature from these languages. I am not interested in how I can make workarounds (using interfaces, cloning, or any other alternative), but rather in the rationale behind the decision.
From a language design perspective, why has this feature been declined?
P.S: I'm using words such as "omitted", which some people may find inadequate, as C# was designed in an additive (rather than subtractive) approach. However, I am using such words because the feature existed in C++ before these languages were designed, so it is omitted in the sense of being removed from a programmer's toolbox.
In this interview, Anders said:
Anders Hejlsberg: Yes. With respect to
const, it's interesting, because we
hear that complaint all the time too:
"Why don't you have const?" Implicit
in the question is, "Why don't you
have const that is enforced by the
runtime?" That's really what people
are asking, although they don't come
out and say it that way.
The reason that const works in C++ is
because you can cast it away. If you
couldn't cast it away, then your world
would suck. If you declare a method
that takes a const Bla, you could pass
it a non-const Bla. But if it's the
other way around you can't. If you
declare a method that takes a
non-const Bla, you can't pass it a
const Bla. So now you're stuck. So you
gradually need a const version of
everything that isn't const, and you
end up with a shadow world. In C++ you
get away with it, because as with
anything in C++ it is purely optional
whether you want this check or not.
You can just whack the constness away
if you don't like it.
I guess primarily because:
it can't properly be enforced, even in C++ (you can cast it)
a single const at the bottom can force a whole chain of const in the call tree
Both can be problematic. But especially the first: if it can't be guaranteed, what use is it? Better options might be:
immutable types (either full immutability, or popsicle immutability)
As to why they did it those involved have said so:
http://blogs.msdn.com/ericgu/archive/2004/04/22/118238.aspx
http://blogs.msdn.com/slippman/archive/2004/01/22/61712.aspx
also mentioned by Raymond Chen
http://blogs.msdn.com/oldnewthing/archive/2004/04/27/121049.aspx
In a multi language system this would have been very complex.
As for Java, how would you have such a property behave? There are already techniques for making objects immutable, which is arguably a better way to achieve this with additional benefits. In fact you can emulate const behaviour by declaring a superclass/superinterface that implements only the methods that don't change state, and then having a subclass/subinterface that implements the mutating methods. By upcasting your mutable class to an instance of class with no write methods, other bits of code cannot modify the object without specifically casting it back to the mutable version (which is equivalent to casting away const).
Even if you don't want the object to be strictly immutable, if you really wanted (which I wouldn't recommend) you could put some kind of 'lock' mode on it so that it could only be mutated when unlocked. Have the lock/unlock methods be private, or protected as appropriate, and you get some level of access control there. Alternatively, if you don't intend for the method taking it as a parameter to modify it at all, pass in a copy of that object, or if copying the entire object is too heavyweight then some other lightweight data object that contains just the necessary information. You could even use dynamic proxies to create a proxy to your object that turn any calls to mutation methods into no-ops.
Basically there are already a whole bunch of ways to prevent a class being mutated, which let you choose one that fits most appropriately into your situation (hint: choose pure immutability wherever possible as it makes the object trivially threadsafe and easier to reason with in general). There are no obvious semantics for how const could be implemented that would be an improvement on these techniques, it would be another thing to learn that would either lack flexibility, or be so flexible as to be useless.
That is, unless I've missed something, which is entirely possible. :-)
Java have its own version of const; final. Joshua Bloch describes in his Effective Java
how you effectively use the final keyword. (btw, const is a reserved keyword in Java, for future discrepancies)
I have a number of data classes representing various entities.
Which is better: writing a generic class (say, to print or output XML) using generics and interfaces, or writing a separate class to deal with each data class?
Is there a performance benefit or any other benefit (other than it saving me the time of writing separate classes)?
There's a significant performance benefit to using generics -- you do away with boxing and unboxing. Compared with developing your own classes, it's a coin toss (with one side of the coin weighted more than the other). Roll your own only if you think you can out-perform the authors of the framework.
Not only yes, but HECK YES. I didn't believe how big of a difference they could make. We did testing in VistaDB after a rewrite of a small percentage of core code that used ArrayLists and HashTables over to generics. 250% or more was the speed improvement.
Read my blog about the testing we did on generics vs weak type collections. The results blew our mind.
I have started rewriting lots of old code that used the weakly typed collections into strongly typed ones. One of my biggest grips with the ADO.NET interface is that they don't expose more strongly typed ways of getting data in and out. The casting time from an object and back is an absolute killer in high volume applications.
Another side effect of strongly typing is that you often will find weakly typed reference problems in your code. We found that through implementing structs in some cases to avoid putting pressure on the GC we could further speed up our code. Combine this with strongly typing for your best speed increase.
Sometimes you have to use weakly typed interfaces within the dot net runtime. Whenever possible though look for ways to stay strongly typed. It really does make a huge difference in performance for non trivial applications.
Generics in C# are truly generic types from the CLR perspective. There should not be any fundamental difference between the performance of a generic class and a specific class that does the exact same thing. This is different from Java Generics, which are more of an automated type cast where needed or C++ templates that expand at compile time.
Here's a good paper, somewhat old, that explains the basic design:
"Design and Implementation of Generics for the
.NET Common Language Runtime".
If you hand-write classes for specific tasks chances are you can optimize some aspects where you would need additional detours through an interface of a generic type.
In summary, there may be a performance benefit but I would recommend the generic solution first, then optimize if needed. This is especially true if you expect to instantiate the generic with many different types.
I did some simple benchmarking on ArrayList's vs Generic Lists for a different question: Generics vs. Array Lists, your mileage will vary, but the Generic List was 4.7 times faster than the ArrayList.
So yes, boxing / unboxing are critical if you are doing a lot of operations. If you are doing simple CRUD stuff, I wouldn't worry about it.
Generics are one of the way to parameterize code and avoid repetition. Looking at your program description and your thought of writing a separate class to deal with each and every data object, I would lean to generics. Having a single class taking care of many data objects, instead of many classes that do the same thing, increases your performance. And of course your performance, measured in the ability to change your code, is usually more important than the computer performance. :-)
According to Microsoft, Generics are faster than casting (boxing/unboxing primitives) which is true.
They also claim generics provide better performance than casting between reference types, which seems to be untrue (no one can quite prove it).
Tony Northrup - co-author of MCTS 70-536: Application Development Foundation - states in the same book the following:
I haven’t been able to reproduce the
performance benefits of generics;
however, according to Microsoft,
generics are faster than using
casting. In practice, casting proved
to be several times faster than using
a generic. However, you probably won’t
notice performance differences in your
applications. (My tests over 100,000
iterations took only a few seconds.)
So you should still use generics
because they are type-safe.
I haven't been able to reproduce such performance benefits with generics compared to casting between reference types - so I'd say the performance gain is "supposed" more than "significant".
if you compare a generic list (for example) to a specific list for exactly the type you use then the difference is minimal, the results from the JIT compiler are almost the same.
if you compare a generic list to a list of objects then there is significant benefits to the generic list - no boxing/unboxing for value types and no type checks for reference types.
also the generic collection classes in the .net library were heavily optimized and you are unlikely to do better yourself.
In the case of generic collections vs. boxing et al, with older collections like ArrayList, generics are a performance win. But in the vast majority of cases this is not the most important benefit of generics. I think there are two things that are of much greater benefit:
Type safety.
Self documenting aka more readable.
Generics promote type safety, forcing a more homogeneous collection. Imagine stumbling across a string when you expect an int. Ouch.
Generic collections are also more self documenting. Consider the two collections below:
ArrayList listOfNames = new ArrayList();
List<NameType> listOfNames = new List<NameType>();
Reading the first line you might think listOfNames is a list of strings. Wrong! It is actually storing objects of type NameType. The second example not only enforces that the type must be NameType (or a descendant), but the code is more readable. I know right away that I need to go find TypeName and learn how to use it just by looking at the code.
I have seen a lot of these "does x perform better than y" questions on StackOverflow. The question here was very fair, and as it turns out generics are a win any way you skin the cat. But at the end of the day the point is to provide the user with something useful. Sure your application needs to be able to perform, but it also needs to not crash, and you need to be able to quickly respond to bugs and feature requests. I think you can see how these last two points tie in with the type safety and code readability of generic collections. If it were the opposite case, if ArrayList outperformed List<>, I would probably still take the List<> implementation unless the performance difference was significant.
As far as performance goes (in general), I would be willing to bet that you will find the majority of your performance bottlenecks in these areas over the course of your career:
Poor design of database or database queries (including indexing, etc),
Poor memory management (forgetting to call dispose, deep stacks, holding onto objects too long, etc),
Improper thread management (too many threads, not calling IO on a background thread in desktop apps, etc),
Poor IO design.
None of these are fixed with single-line solutions. We as programmers, engineers and geeks want to know all the cool little performance tricks. But it is important that we keep our eyes on the ball. I believe focusing on good design and programming practices in the four areas I mentioned above will further that cause far more than worrying about small performance gains.
Generics are faster!
I also discovered that Tony Northrup wrote wrong things about performance of generics and non-generics in his book.
I wrote about this on my blog:
http://andriybuday.blogspot.com/2010/01/generics-performance-vs-non-generics.html
Here is great article where author compares performance of generics and non-generics:
nayyeri.net/use-generics-to-improve-performance
If you're thinking of a generic class that calls methods on some interface to do its work, that will be slower than specific classes using known types, because calling an interface method is slower than a (non-virtual) function call.
Of course, unless the code is the slow part of a performance-critical process, you should focus of clarity.
See Rico Mariani's Blog at MSDN too:
http://blogs.msdn.com/ricom/archive/2005/08/26/456879.aspx
Q1: Which is faster?
The Generics version is considerably
faster, see below.
The article is a little old, but gives the details.
Not only can you do away with boxing but the generic implementations are somewhat faster than the non generic counterparts with reference types due to a change in the underlying implementation.
The originals were designed with a particular extension model in mind. This model was never really used (and would have been a bad idea anyway) but the design decision forced a couple of methods to be virtual and thus uninlineable (based on the current and past JIT optimisations in this regard).
This decision was rectified in the newer classes but cannot be altered in the older ones without it being a potential binary breaking change.
In addition iteration via foreach on an List<> (rather than IList<>) is faster due to the ArrayList's Enumerator requiring a heap allocation. Admittedly this did lead to an obscure bug
I know that in C# 3.0 you can do some functional programming magic with Linq and lambda expression and all that stuff. However, is it really possible to go completely "pure" functional in C#? By "pure" I mean having methods that are pure (always gives the same output for the same input) and completely free of side-effects. How do we get around the fact that we do not even have immutable integer type in C#?
If you want to program in a pure functional way, there is nothing stopping you.
On the other hand, if you have some program, there is no magic flag you can flip to force the program to behave in a pure functional way.
For ints (immutable)
If you use an int as a parameter, it is passed by value. Any changes are not propogated to the caller.
If you use an int declared in one method's scope in a closure within the method, than that int variable is shared. In this case, one must either pledge not to modify the int (programmer enforced), or simply not use an int in this way.
And if you truly need an immutable int, have you seen the readonly keyword?
Have you looked into F#? It seems much more along the lines of what you are talking about. C# just really isn't designed with functional programming in mind, and therefore won't really give you any of the benefits that are normally associated with a functional language.
Unfortunately no - C# is not a pure functional language and it does not intend to be. What has happened is that the C# team has seen that there are benefits to adding certain functionally-styled constructs and syntax to the language.
Functional purity is better found in other places (Lisp derivatives like Common Lisp and Scheme are good places to start).