While refactoring some C# classes, I've run into classes that implement IDisposable.
Without thinking, I have created partial class files for each class that implements IDisposable interface.
E.g.) For Stamper.cs -> Stamper.cs + Stamper.Dispose.cs
where Stamper.cs contains actual logic for stamping
and Stamper.Dispose.cs that contains dispose logic
// Stamper.cs
public partial class Stamper
{
// actual logic
}
// Stamper.Dispose.cs
public partial class Stamper: IDisposable
{
// Implement IDisposable
}
When I looked at the code, Stamper.cs now looks a lot cleaner and readable (now about 52 lines instead of 100 lines where around 50 lines was simply a clean-up dispose code)
Am I going too far with this?
*EDIT: Thanks folks for your opinions - I have decided to put two files together into one.
The Problem I had faced was that I was actually forgetting to update IDisposable implementation after updating actual logic.
Moreover there wasn't much problem navigating between method in the source code.
The first reason seems more than a reason enough to stick with one file solution in my specific case.
Yes, too far. Whats wrong with just sticking a #Region around the code and folding it so you cant see it?
It seems about as arbitrary as creating a partial class for constructor logic. Now I have to look at two files to grock that class. Partial classes are only really worth it for designer stuff...
I would prefer to see the dispose logic in the same file as the resources that warrant implementing IDisposable. Whilst there's an element of subjectivity, I'd say it's too far
I think your solution is unsound. Partial classes should usually only be used to separate developer code from generator code. Regions usually do a better job of adding structure to your code.
If your clean up procedure is heavy, it's acceptable, but not ideal.
It might be a good habit for boiler plate such as exposed events, heavy serialization methods and in your case memory management.
I prefer partial classes than outlines (#region). If you have to use partial class or code outlining to make your code readable, this is usually a sign that the code needs to be changed. Tear the class appart and only as a last resort use partial class (or region) if the code is absolutly necessary for upkeeping that class.
In your case, you could use a class that thinly wraps the unmanaged resource and expose a single Dispose. Then in your other class, use the managed object and Dispose it with no logic.
If your class is only a thin wrap, then I'd say your method is overkill since the whole point of the class is to dispose an unmanaged resource.
Kind of an odd question since it only has an impact on the developer, making it completely up to personal preference. I can only tell you what I would prefer and that would be that I would do it if a significant amount of logic was in the dispose portion.
Personally I try to keep my instantiation/initialization logic and my cleanup/disposal logic side-by-side, it's a good reminder.
As for partial classes, the only time I use them is if a class is very large and can be categorized into groups of methods. Hiding designer code is great too.
I'd favor using a partial class when, and only when, the code in question was computer-generated. If you have many classes which share similar code (which for various reasons has to be repeated, rather than being pulled out into its own class) it may be useful to have a few templates and a program to generate the code based upon such templates. Under that scenario, the templates would be regarded as source files and then generated files as intermediate object-ish code. It would seem entirely appropriate to pull out the template-generated code into partial classes.
In vb.net, such an approach might be nice to allow field declaration, initialization, and cleanup to be safely handled together within an IDisposable object. A moderate amount of boilerplate code is required, but field declarations after that are pretty clean. For example:
' Assuming Option Implicit on:
Dim MyThingie = RegDisposable(New DisposableThingie)
' If Implicit wasn't on:
Dim MyThingie As DisposableThingie = RegDisposable(New DisposableThingie)
RegDisposable would be a class member that would add the new DisposableThingie to a list held by the class. The class' Dispose routine would then Dispose all the items in the list.
Unfortunately, there's no clean way to do anything similar in C#, since field initializers cannot make use of the object about to be constructed (in vb.net, field initializers run after the base object is constructed).
Related
This may be a bit of an odd question, and what I have in place now works, but it feels a bit strange to me and I wonder it's because of poor design/architecture. Any thoughts here would be appreciated.
The initial design is in a code base I inherited from someone else. We have a linq-to-sql class (auto generated in the dbml's designer file).
[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.ARCustomers")]
public partial class ARCustomer : INotifyPropertyChanging, INotifyPropertyChanged
{
// variables
// extensibility method defs
// ctor
// properties
// etc.
}
Then another class class called ArCustomer (notice the lower case "r") that is an extended version of the auto-generated class. When I say extended, I mean it has all the properies of the LINQ class, plus a few more that requires some logic to populate.
There are a lot of places in code that we want to take an ARCustomer and turn it into an ArCustomer. So I wrote an extension method (this is what felt strange) on the ArCustomer class.
public static ArCustomer FromDatacontextObject(this ArCustomer customer, ARCustomer datacontextObject)
{
var arCustomer = new ArCustomer();
arCustomer.Id = datacontextObject.ProjectID;
// more of the same
// now populate the other fields that don't exist on the datacontextObject
return arCustomer;
}
It's called as such.
var customerfromDb = accountReceivableRepository.GetCurCustomer(arId);
ArCustomer customer = new ArCustomer();
customer = customer.FromDatacontextObject(customerfromDb);
This feels wrong to me, but I don't know of any better alternatives off the top of my head. (Would a partial class that contains the extended properties work? Populate them in it's constructor?) Or maybe it's fine... I'm interested in a few things...
Am I right in feeling that this is wrong/odd/bad?
Specifically, what are the cons to be found in the solution I've implemented? I feel like one is that I scratch my head too often trying to differentiate between the two classes and figure out which is which.
Are their any pros?
Any better solutions (and why they're better)?
(Unrelated - I hope this kind of question is OK for stack overflow. I almost feel like I'm asking for a mini code review, which can be subjective; on the other hand, I tried to ask some concrete questions and feel I must not be the only developer to have ran into a situation like this ("I have one object and need to turn it into another"), so hopefully there is something to be gained from leaving the thread open).
Thanks guys!
Your instincts serve you well.
Having two classes with the same name (differing only be case) is technically allowed by the C# compiler, but it is a bad idea. Also, it is not CLS compliant.
It is a bad idea for the exact reason that you already stated: readability. Don't underestimate the importance of readability. Personally it is my number one measure of code quality. Readable code tends to have fewer bugs, and is easier to debug/maintain.
The classes generated by LINQ to SQL are already partial classes. You can add a separate code file to define any extra parts that you want. And, this is the preferred method to accomplish what you are describing. It is easier to maintain and understand.
Alternatively, you could create a "ViewModel" class that contains the ARCustomer. (This depends on your architecture).
If you change the extension method to extend the database object you have a more natural API IMO
public static ArCustomer ToDomainObject(this ARCustomer datacontextObject)
{
var arCustomer = new ArCustomer();
arCustomer.Id = datacontextObject.ProjectID;
// more of the same
// now populate the other fields that don't exist on the datacontextObject
return arCustomer;
}
then the data access code looks like this
var customerfromDb = accountReceivableRepository.GetCurCustomer(arId);
ArCustomer customer = customerfromDb.ToDomainObject();
Few days ago I had the same problem. And I did find some discussions on this topic.
These threads might help: Thread one, Thread two
As I figured out, there is no better way to do what you are doing. However, you might try to use reflection to iterate through all the fields in parent object to copy them to relevant fields in child object. Some example code here, And discussion here.
For my problem, ended up going field by field manually, as some of the fields I needed to be deeply cloned, some had to be copied only by reference.
I was wondering if someone could give me an overview of why I would use them and what advantage I would gain in the process.
The biggest use of partial classes is to make life easier for code generators / designers. Partial classes allow the generator to simply emit the code they need to emit and they do not have to deal with user edits to the file. Users are likewise free to annotate the class with new members by having a second partial class. This provides a very clean framework for separation of concerns.
A better way to look at it is to see how designers functioned before partial classes. The WinForms designer would spit out all of the code inside of a region with strongly worded comments about not modifying the code. It had to insert all sorts of heuristics to find the generated code for later processing. Now it can simply open the designer.cs file and have a high degree of confidence that it contains only code relevant to the designer.
Another use is to split the implementation of different interfaces, e.g:
partial class MyClass : IF3
{
// main implementation of MyClass
}
partial class MyClass : IF1
{
// implementation of IF1
}
partial class MyClass : IF2
{
// implementation of IF2
}
Aside from the other answers...
I've found them helpful as a stepping-stone in refactoring god-classes. If a class has multiple responsibilities (especially if it's a very large code-file) then I find it beneficial to add 1x partial class per-responsibility as a first-pass for organizing and then refactoring the code.
This helps greatly because it can help with making the code much more readable without actually effecting the executing behavior. It also can help identify when a responsibility is easy to refactor out or is tightly tangled with other aspects.
However--to be clear--this is still bad code, at the end of development you still want one responsibility per-class (NOT per partial class). It's just a stepping-stone :)
Multiple Developer Using Partial Classes multiple developer can work on the same class
easily.
Code Generator Partial classes are mainly used by code generator to keep
different concerns separate
Partial Methods Using Partial Classes you can also define Partial methods as well where a developer can simply define the method and the other developer can implement that.
Partial Method Declaration only Even the code get compiled with method declaration only and if the implementation
of the method isn't present compiler can safely remove that piece of
code and no compile time error will occur.
To verify point 4. Just create a winform project and include this line after the Form1 Constructor and try to compile the code
partial void Ontest(string s);
Here are some points to consider while implementing partial classes:-
Use partial keyword in each part of partial class.
The name of each part of partial class should be the same but the source file name for each part of partial class can be different.
All parts of a partial class should be in the same namespace.
Each part of a partial class should be in the same assembly or DLL, in other words you can't create a partial class in source files from a different class library project.
Each part of a partial class must have the same accessibility. (i.e: private, public or protected)
If you inherit a class or interface on a partial class then it is inherited by all parts of that partial class.
If a part of a partial class is sealed then the entire class will be sealed.
If a part of partial class is abstract then the entire class will be considered an abstract class.
One great use is separating generated code from hand-written code that belong in the same class.
For example since LINQ to SQL uses partial classes you can write your own implementation of certain pieces of functionality (like Many-to-Many relationships) and those pieces of custom code won't get overwritten when you re-generate the code.
The same goes for WinForms code. All the Designer generated code goes in one file that you generally don't touch. Your hand-written code goes in another file. That way, when you change something in Designer, your changes don't get blown away.
It is true that Partial Class is used in auto code generation, one use can be maintaining a large class file which might have thousand lines of code. You never know your class might end up with 10 thousand lines and you don't want to create a new class with different name.
public partial class Product
{
// 50 business logic embedded in methods and properties..
}
public partial class Product
{
// another 50 business logic embedded in methods and properties..
}
//finally compile with product.class file.
Another possible use could be that more than one developer can work on the same class as they are stored at different places. People might laugh but you never know it can be handful sometimes.
Product1.cs
public partial class Product
{
//you are writing the business logic for fast moving product
}
Product2.cs
public partial class Product
{
// Another developer writing some business logic...
}
Hope it makes sense!
Partial classes span multiple files.
How can you use the partial modifier on a C# class declaration?
With partial classes, you can physically separate a class into multiple files. This is often done by code generators.
Example
With normal C# classes, you cannot declare a class in two separate files in the same project. But with the partial modifier, you can.
This is useful if one file is commonly edited and the other is machine-generated or rarely edited.
Here's an example to clarify:
class Program
{
static void Main()
{
A.A1();
A.A2();
}
}
Contents of file A1.cs: C#
using System;
partial class A
{
public static void A1()
{
Console.WriteLine("A1");
}
}
Contents of file A2.cs: C#
using System;
partial class A
{
public static void A2()
{
Console.WriteLine("A2");
}
}
Output:
A1
A2
Partial is required here.
If you remove the partial modifier, you will get an error containing this text:
[The namespace '<global namespace>' already contains a definition for 'A'].
Tip:
To fix this, you can either use the partial keyword, or change one of the class names.
How does the C# compiler deal with partial classes?
If you disassemble the above program (using IL Disassembler), you will see that the files A1.cs and A2.cs are eliminated. You will find that the class A is present.
Class A will contain the methods A1 and A2 in the same code block. The two classes were merged into one.
Compiled result of A1.cs and A2.cs: C#
internal class A
{
// Methods
public static void A1()
{
Console.WriteLine("A1");
}
public static void A2()
{
Console.WriteLine("A2");
}
}
Summary
Partial classes can simplify certain C# programming situations.
They are often used in Visual Studio when creating Windows Forms/WPF programs.
The machine-generated C# code is separate.
Or You could find the whole description here.
keep everything as clean as possible when working with huge classes, or when working on a team, you can edit without overriding (or always commiting changes)
The main use for partial classes is with generated code. If you look at the WPF (Windows Presentation Foundation) network, you define your UI with markup (XML). That markup is compiled into partial classes. You fill in code with partial classes of your own.
As an alternative to pre-compiler directives.
If you use pre-compiler directives (namely #IF DEBUG) then you end up with some gnarly looking code intermingled with your actual Release code.
You can create a seperate partial-class to contain this code, and either wrap the entire partial class in a directive, or omit that code-file from being sent to the compiler (effectively doing the same).
If you have a sufficiently large class that doesn't lend itself to effective refactoring, separating it into multiple files helps keep things organized.
For instance, if you have a database for a site containing a discussion forum and a products system, and you don't want to create two different providers classes (NOT the same thing as a proxy class, just to be clear), you can create a single partial class in different files, like
MyProvider.cs - core logic
MyProvider.Forum.cs - methods pertaining specifically to the forum
MyProvider.Product.cs - methods for products
It's just another way to keep things organized.
Also, as others have said, it's about the only way to add methods to a generated class without running the risk of having your additions destroyed the next time the class is regenerated. This comes in handy with template-generated (T4) code, ORMs, etc.
Most people remark that partial should only be used for a class that has a generated code file or for interfaces. I disagree, and here is why.
For one example, let's look at the C# System.Math class... that's class. I would not attempt to stuff 70+ methods all into the same single code file. It would be a nightmare to maintain.
Placing each math method into individual partial class files, and all code files into a Math folder in the project, would be significantly cleaner organization.
The same could/would hold true for many other classes that have a large amount of diverse functionality. For example a class for managing the PrivateProfile API might benefit by being split into a clean set of partial class files in a single project folder.
Personally, I also split what most people call "helper" or "utility" classes into individual partial files for each method or method functional group. For example on one project the string helper class has almost 50 methods. That would be a long unwieldy code file even using regions. It is significantly easier to maintain using individual partial class files for each method.
I would just be careful using partial classes and keep all code file layout consistent throughout the project when doing this. Such as placing any class public enums and class private members into a Common.cs or similarly named file in the folder, instead of spreading them out across the files unless they are specific to only the partial file they are contained in.
Keep in mind that when you split a class into separate files you also lose the ability to use the text editor splitter bar that lets you view two different sections of a current file simultaneously.
Another use i saw is,
Extending a big abstract class regarding data access logic ,
i have various files with names Post.cs,Comment.cs,Pages.cs...
in Post.cs
public partial class XMLDAO :BigAbstractClass
{
// CRUD methods of post..
}
in Comment.cs
public partial class XMLDAO :BigAbstractClass
{
// CRUD methods of comment..
}
in Pages.cs
public partial class XMLDAO :BigAbstractClass
{
// CRUD methods of Pages..
}
Service references are another example where partial classes are useful to separate generated code from user-created code.
You can "extend" the service classes without having them overwritten when you update the service reference.
Partial classes make it possible to add functionality to a suitably-designed program merely by adding source files. For example, a file-import program could be designed so that one could add different types of known files by adding modules that handle them. For example, the main file type converter could include a small class:
Partial Public Class zzFileConverterRegistrar
Event Register(ByVal mainConverter as zzFileConverter)
Sub registerAll(ByVal mainConverter as zzFileConverter)
RaiseEvent Register(mainConverter)
End Sub
End Class
Each module that wishes to register one or more types of file converter could include something like:
Partial Public Class zzFileConverterRegistrar
Private Sub RegisterGif(ByVal mainConverter as zzFileConverter) Handles Me.Register
mainConverter.RegisterConverter("GIF", GifConverter.NewFactory))
End Sub
End Class
Note that the main file converter class isn't "exposed"--it just exposes a little stub class that add-in modules can hook to. There is a slight risk of naming conflicts, but if each add-in module's "register" routine is named according to the type of file it deals with, they probably shouldn't pose a problem. One could stick a GUID in the name of the registration subroutine if one were worried about such things.
Edit/Addendum
To be clear, the purpose of this is to provide a means by which a variety of separate classes can let a main program or class know about them. The only thing the main file converter will do with zzFileConverterRegistrar is create one instance of it and call the registerAll method which will fire the Register event. Any module that wants to hook that event can execute arbitrary code in response to it (that's the whole idea) but there isn't anything a module could do by improperly extending the zzFileConverterRegistrar class other than define a method whose name matches that of something else. It would certainly be possible for one improperly-written extension to break another improperly-written extension, but the solution for that is for anyone who doesn't want his extension broken to simply write it properly.
One could, without using partial classes, have a bit of code somewhere within the main file converter class, which looked like:
RegisterConverter("GIF", GifConvertor.NewFactory)
RegisterConverter("BMP", BmpConvertor.NewFactory)
RegisterConverter("JPEG", JpegConvertor.NewFactory)
but adding another converter module would require going into that part of the converter code and adding the new converter to the list. Using partial methods, that is no longer necessary--all converters will get included automatically.
Partial classes recently helped with source control where multiple developers were adding to one file where new methods were added into the same part of the file (automated by Resharper).
These pushes to git caused merge conflicts. I found no way to tell the merge tool to take the new methods as a complete code block.
Partial classes in this respect allows for developers to stick to a version of their file, and we can merge them back in later by hand.
example -
MainClass.cs - holds fields, constructor, etc
MainClass1.cs - a developers new code as they implement
MainClass2.cs - is another developers class for their new code.
From MSDN:
1.At compile time, attributes of partial-type definitions are merged. For example, consider the following declarations:
[SerializableAttribute]
partial class Moon { }
[ObsoleteAttribute]
partial class Moon { }
They are equivalent to the following declarations:
[SerializableAttribute]
[ObsoleteAttribute]
class Moon { }
The following are merged from all the partial-type definitions:
XML comments
interfaces
generic-type parameter attributes
class attributes
members
2.Another thing, nested partial classes can be also partial:
partial class ClassWithNestedClass
{
partial class NestedClass { }
}
partial class ClassWithNestedClass
{
partial class NestedClass { }
}
Here is a list of some of the advantages of partial classes.
You can separate UI design code and business logic code so that it is easy to read and understand. For example you are developing an web application using Visual Studio and add a new web form then there are two source files, "aspx.cs" and "aspx.designer.cs" . These two files have the same class with the partial keyword. The ".aspx.cs" class has the business logic code while "aspx.designer.cs" has user interface control definition.
When working with automatically generated source, the code can be added to the class without having to recreate the source file. For example you are working with LINQ to SQL and create a DBML file. Now when you drag and drop a table it creates a partial class in designer.cs and all table columns have properties in the class. You need more columns in this table to bind on the UI grid but you don't want to add a new column to the database table so you can create a separate source file for this class that has a new property for that column and it will be a partial class. So that does affect the mapping between database table and DBML entity but you can easily get an extra field. It means you can write the code on your own without messing with the system generated code.
More than one developer can simultaneously write the code for the class.
You can maintain your application better by compacting large classes. Suppose you have a class that has multiple interfaces so you can create multiple source files depending on interface implements. It is easy to understand and maintain an interface implemented on which the source file has a partial class.
I find it disturbing that the word 'cohesion' does not appear anywhere in these posts (until now).
And I'm also disturbed that anyone thinks enabling or encouraging huge classes and methods is somehow a good thing.
If you're trying to understand and maintain a code-base 'partial' sucks.
Whenever I have a class that contains a nested class that is of any significant size/complexity, I mark the class as partial and put the nested class in a separate file. I name the file containing the nested class using the rule: [class name].[nested class name].cs.
The following MSDN blog explains using partial classes with nested classes for maintainability: http://blogs.msdn.com/b/marcelolr/archive/2009/04/13/using-partial-classes-with-nested-classes-for-maintainability.aspx
I know this question is really old but I would just like to add my take on partial classes.
One reason that I personally use partial classes is when I'm creating bindings for a program, especially state machines.
For example, OpenGL is a state machine, there are heaps of methods that can all be changed globally, however, in my experience binding something similar to OpenGL where there are so many methods, the class can easily exceed 10k LOC.
Partial classes will break this down for me and help me with finding methods quickly.
Partial classes are primarily introduced to help Code generators, so we (users) don't end up loosing all our work / changes to the generated classes like ASP.NET's .designer.cs class each time we regenerate, almost all new tools that generate code LINQ, EntityFrameworks, ASP.NET use partial classes for generated code, so we can safely add or alter logic of these generated codes taking advantage of Partial classes and methods, but be very carefully before you add stuff to the generated code using Partial classes its easier if we break the build but worst if we introduce runtime errors. For more details check this https://web.archive.org/web/20211020111732/https://www.4guysfromrolla.com/articles/071509-1.aspx
I note two usages which I couldn't find explicitly in the answers.
Grouping Class Items
Some developers use comments to separate different "parts" of their class. For example, a team might use the following convention:
public class MyClass{
//Member variables
//Constructors
//Properties
//Methods
}
With partial classes, we can go a step further, and split the sections into separate files. As a convention, a team might suffix each file with the section corresponding to it. So in the above we would have something like: MyClassMembers.cs, MyClassConstructors.cs, MyClassProperties.cs, MyClassMethods.cs.
As other answers alluded to, whether or not it's worth splitting the class up probably depends on how big the class is in this case. If it's small, it's probably easier to have everything in one master class. But if any of those sections get too big, its content can be moved to a separate partial class, in order to keep the master class neat. A convention in that case might be to leave a comment in saying something like "See partial class" after the section heading e.g.:
//Methods - See partial class
Managing Scope of Using statements / Namespace
This is probably a rare occurrence, but there might be a namespace collision between two functions from libraries that you want to use. In a single class, you could at most use a using clause for one of these. For the other you'd need a fully qualified name or an alias. With partial classes, since each namespace & using statements list is different, one could separate the two sets of functions into two separate files.
Reading some article about singleton, I stopped at the point saying: "Do not allow to crate copy of existing instance".
I realized that I do not know how would I do that! Could you tell me, please, how could I copy existing instance of class?
And the second one: deserializaition. How it could be dangerous?
And for both - how to deny creating copies or deserialization?
Thanks
There are objects with something like a Clone or a Copy method. The idea behind it that it will take the current values of the object and make a new one. The defeats the purpose of a singleton object, because suddenly someone can create a second copy of it.
Another possible way of creating a copy of the object, would be to serialize the object and then de-serialize it to create another copy. So you probably want to mark the singleton object as not serializable.
Using serialization/deserialization, you could store the object somewhere and then restore it. That way, you will have two objects. Any changes made to the singleton in the meantime would not be reflected in your new copy.
Afterwards, when you now try to get/set something using the singleton object, you might change it in/get it from the one object or the other. Obviously that can cause all sorts of (sometimes very hard to debug) problems.
EDIT: To create a singleton in C#, see the explanation at http://www.yoda.arachsys.com/csharp/singleton.html
As for serialization: You have to explicitely enable it by including the SerializableAttribute. So simply don't mark your class with it. Note that there is no NonSerializableAttribute for classes, only for fields. It is used when you enabled serialization, but want to deny it for certain parts of the class.
EDIT2: To deny XML-serialization, you could implement IXmlSerializable on the class. Then simply either have empty implementations or throw exceptions from the member methods.
As has already been mentioned:
You don't want to make a singleton serializable or copy/clone-able because then you can make more than one object, which defeats the purpose of the singleton.
To prevent serialization in c# is easy - don't mark the class as [Serializable]
To prevent copying/cloning of your singleton you could try changing it to a static class so that can't be instantiated (in the normal way) if that's practical. I'm not sure if the class is technically a singleton any more then.
Another way (probably better) is detailed in Item 13 of Bill Wagner's Effective C#. i.e. using a static constructor and making your singleton a read only property of your static class.
Example:
public class SingletonExample
{
private static readonly SingletonExample singleInstance
static SingletonExample()
{
singleInstance = new SingletonExample();
}
public static SingletonExample Instance
{
get { return singleInstance; }
}
private SingletonExample()
{
}
}
There are a few things to look out for, like Kevin mentioned any sort of .Clone() or .Copy() methods. If your building the class your self, then be carful with the .MemberwiseClone() method as it will make shallow copies of the object.
As far as serialization. Preventing general serialization can be done by not tagging [SerializableAttribute()] to you class. I'm not sure there is a way to prevent XmlSerialzation, directly. But there are a few things you could do to prevent this if your building the class.
If you're building the class, and you do not provide a default constructor then the XmlDeserializer will not work as it uses the default constructor to rebuild the object. I belive this funcitonality has changed in 4.0 however, so you may want to look more into that. Using the [XmlIgnore] Attribute on yoru fields and properties will render the serialzation useless as well.
The important part here is that the person trying to do this understand it shouldn't be done, not that it can't. If someone really wants to do serialization/deserialization on your class, then you can't stop all avenues as he can implement his own serialzation/deserialization of your object. Also serialzation of singletons is sometimes intended such as the cases of application settings or custom settings. The intent is to inform somehow the person trying to serialize/deserialize not to do so.
I work at a company where some require justification for the use of an Interface in our code (Visual Studio C# 3.5).
I would like to ask for an Iron Clad reasoning that interfaces are required for. (My goal is to PROVE that interfaces are a normal part of programming.)
I don't need convincing, I just need a good argument to use in the convincing of others.
The kind of argument I am looking for is fact based, not comparison based (ie "because the .NET library uses them" is comparison based.)
The argument against them is thus: If a class is properly setup (with its public and private members) then an interface is just extra overhead because those that use the class are restricted to public members. If you need to have an interface that is implemented by more than 1 class then just setup inheritance/polymorphism.
Code decoupling. By programming to interfaces you decouple the code using the interface from the code implementing the interface. This allows you to change the implementation without having to refactor all of the code using it. This works in conjunction with inheritance/polymorphism, allowing you to use any of a number of possible implementations interchangeably.
Mocking and unit testing. Mocking frameworks are most easily used when the methods are virtual, which you get by default with interfaces. This is actually the biggest reason why I create interfaces.
Defining behavior that may apply to many different classes that allows them to be used interchangeably, even when there isn't a relationship (other than the defined behavior) between the classes. For example, a Horse and a Bicycle class may both have a Ride method. You can define an interface IRideable that defines the Ride behavior and any class that uses this behavior can use either a Horse or Bicycle object without forcing an unnatural inheritance between them.
The argument against them is thus: If
a class is properly setup (with its
public and private members) then an
interface is just extra overhead
because those that use the class are
restricted to public members. If you
need to have an interface that is
implemented by more than 1 class then
just setup inheritance/polymorphism.
Consider the following code:
interface ICrushable
{
void Crush();
}
public class Vehicle
{
}
public class Animal
{
}
public class Car : Vehicle, ICrushable
{
public void Crush()
{
Console.WriteLine( "Crrrrrassssh" );
}
}
public class Gorilla : Animal, ICrushable
{
public void Crush()
{
Console.WriteLine( "Sqqqquuuuish" );
}
}
Does it make any sense at all to establish a class hierarchy that relates Animals to Vehicles even though both can be crushed by my giant crushing machine? No.
In addition to things explained in other answers, interfaces allow you simulate multiple inheritance in .NET which otherwise is not allowed.
Alas as someone said
Technology is dominated by two types of people: those who understand what they do not manage, and those who manage what they do not understand.
To enable unit testing of the class.
To track dependencies efficiently (if the interface isn't checked out and touched, only the semantics of the class can possibly have changed).
Because there is no runtime overhead.
To enable dependency injection.
...and perhaps because it's friggin' 2009, not the 70's, and modern language designers actually have a clue about what they are doing?
Not that interfaces should be thrown at every class interface: just those which are central to the system, and which are likely to experience significant change and/or extension.
Interfaces and abstract classes model different things. You derive from a class when you have an isA relationship so the base class models something concrete. You implement an interface when your class can perform a specific set of tasks.
Think of something that's Serializable, it doesn't really make sense (from a design/modelling point of view) to have a base class called Serializable as it doesn't make sense to say something isA Serializable. Having something implement a Serializable interface makes more sense as saying 'this is something the class can do, not what the class is'
Interfaces are not 'required for' at all, it's a design decision. I think you need to convince yourself, why, on a case-by-case basis, it is beneficial to use an interface, because there IS an overhead in adding an interface. On the other hand, to counter the argument against interfaces because you can 'simply' use inheritance: inheritance has its draw backs, one of them is that - at least in C# and Java - you can only use inheritance once(single inheritance); but the second - and maybe more important - is that, inheritance requires you to understand the workings of not only the parent class, but all of the ancestor classes, which makes extension harder but also more brittle, because a change in the parent class' implementation could easily break the subclasses. This is the crux of the "composition over inheritance" argument that the GOF book taught us.
You've been given a set of guidelines that your bosses have thought appropriate for your workplace and problem domain. So to be persuasive about changing those guidelines, it's not about proving that interfaces are a good thing in general, it's about proving that you need them in your workplace.
How do you prove that you need interfaces in the code you write in your workplace? By finding a place in your actual codebase (not in some code from somebody else's product, and certainly not in some toy example about Duck implementing the makeNoise method in IAnimal) where an interface-based solution is better than an inheritance-based solution. Show your bosses the problem you're facing, and ask whether it makes sense to modify the guidelines to accommodate situations like that. It's a teachable moment where everyone is looking at the same facts instead of hitting each other over the head with generalities and speculations.
The guideline seems to be driven by a concern about avoiding overengineering and premature generalisation. So if you make an argument along the lines of we should have an interface here just in case in future we have to..., it's well-intentioned, but for your bosses it sets off the same over-engineering alarm bells that motivated the guideline in the first place.
Wait until there's a good objective case for it, that goes both for the programming techniques you use in production code and for the things you start arguments with your managers about.
Test Driven Development
Unit Testing
Without interfaces producing decoupled code would be a pain. Best practice is to code against an interface rather than a concrete implementation. Interfaces seem rubbish at first but once you discover the benefits you'll always use them.
You can implement multiple interfaces. You cannot inherit from multiple classes.
..that's it. The points others are making about code decoupling and test-driven development don't get to the crux of the matter because you can do those things with abstract classes too.
Interfaces allow you to declare a concept that can be shared amongst many types (IEnumerable) while allowing each of those types to have its own inheritance hierarchy.
In this case, what we're saying is "this thing can be enumerated, but that is not its single defining characteristic".
Interfaces allow you to make the minimum amount of decisions necessary when defining the capabilities of the implementer. When you create a class instead of an interface, you have already declared that your concept is class-only and not usable for structs. You also make other decisions when declaring members in a class, such as visibility and virtuality.
For example, you can make an abstract class with all public abstract members, and that is pretty close to an interface, but you have declared that concept as overridable in all child classes, whereas you wouldn't have to have made that decision if you used an interface.
They also make unit testing easier, but I don't believe that is a strong argument, since you can build a system without unit tests (not recommended).
If your shop is performing automated testing, interfaces are a great boon to dependency injection and being able to test a unit of software in isolation.
The problem with the inheritance argument is that you'll either have a gigantic god class or a hierarchy so deep, it'll make your head spin. On top of that, you'll end up with methods on a class you don't need or don't make any sense.
I see a lot of "no multiple inheritance" and while that's true, it probably won't phase your team because you can have multiple levels of inheritance to get what they'd want.
An IDisposable implementation comes to mind. Your team would put a Dispose method on the Object class and let it propagate through the system whether or not it made sense for an object or not.
An interface declares a contract that any object implementing it will adhere to. This makes ensuring quality in code so much easier than trying to enforce written (not code) or verbal structure, the moment a class is decorated with the interface reference the requirements/contract is clear and the code won't compile till you've implemented that interface completely and type-safe.
There are many other great reasons for using Interfaces (listed here) but probably don't resonate with management quite as well as a good, old-fashioned 'quality' statement ;)
Well, my 1st reaction is that if you've to explain why you need interfaces, it's a uphill battle anyways :)
that being said, other than all the reasons mentioned above, interfaces are the only way for loosely coupled programming, n-tier architectures where you need to update/replace components on the fly etc. - in personal experience however that was too esoteric a concept for the head of architecture team with the result that we lived in dll hell - in the .net world no-less !
Please forgive me for the pseudo code in advance!
Read up on SOLID principles. There are a few reasons in the SOLID principles for using Interfaces. Interfaces allow you to decouple your dependancies on implementation. You can take this a step further by using a tool like StructureMap to really make the coupling melt away.
Where you might be used to
Widget widget1 = new Widget;
This specifically says that you want to create a new instance of Widget. However if you do this inside of a method of another object you are now saying that the other object is directly dependent on the use of Widget. So we could then say something like
public class AnotherObject
{
public void SomeMethod(Widget widget1)
{
//..do something with widget1
}
}
We are still tied to the use of Widget here. But at least this is more testable in that we can inject the implementation of Widget into SomeMethod. Now if we were to use an Interface instead we could further decouple things.
public class AnotherObject
{
public void SomeMethod(IWidget widget1)
{
//..do something with widget1
}
}
Notice that we are now not requiring a specific implementation of Widget but instead we are asking for anything that conforms to IWidget interface. This means that anything could be injected which means that in the day to day use of the code we could inject an actual implementation of Widget. But this also means that when we want to test this code we could inject a fake/mock/stub (depending on your understanding of these terms) and test our code.
But how can we take this further. With the use of StructureMap we can decouple this code even more. With the last code example our calling code my look something like this
public class AnotherObject
{
public void SomeMethod(IWidget widget1)
{
//..do something with widget1
}
}
public class CallingObject
{
public void AnotherMethod()
{
IWidget widget1 = new Widget();
new AnotherObject().SomeMethod(widget1);
}
}
As you can see in the above code we removed the dependency in the SomeMethod by passing in an object that conforms to IWidget. But in the CallingObject().AnotherMethod we still have the dependency. We can use StructureMap to remove this dependency too!
[PluginFamily("Default")]
public interface IAnotherObject
{
...
}
[PluginFamily("Default")]
public interface ICallingObject
{
...
}
[Pluggable("Default")]
public class AnotherObject : IAnotherObject
{
private IWidget _widget;
public AnotherObject(IWidget widget)
{
_widget = widget;
}
public void SomeMethod()
{
//..do something with _widget
}
}
[Pluggable("Default")]
public class CallingObject : ICallingObject
{
public void AnotherMethod()
{
ObjectFactory.GetInstance<IAnotherObject>().SomeMethod();
}
}
Notice that no where in the above code are we instantiating an actual implementation of AnotherObject. Because everything is wired for StructurMap we can allow StructureMap to pass in the appropriate implementations depending on when and where the code is ran. Now the code is truely flexible in that we can specify via configuration or programatically in a test which implementation we want to use. This configuration can be done on the fly or as part of a build process, etc. But it doesn't have to be hard wired anywhere.
Appologies as this doesn't answer your question regarding a case for Interfaces.
However I suggest getting the person in question to read..
Head First Design Patterns
-- Lee
I don't understand how its extra overhead.
Interfaces provide flexibility, manageable code, and reusability. Coding to an interface you don't need to worry about the concreted implementation code or logic of the certain class you are using. You just expect a result. Many class have different implementation for the same feature thing (StreamWriter,StringWriter,XmlWriter)..you do not need to worry about how they implement the writing, you just need to call it.
I have an initialization class that preloads content into a variable (probably a list or array). There will only be one instance of this initialization class but there will be many classes that need to access the preloaded content.
The problem is not many of them are related and none of them extend my initialization class. I thought about this for a bit and decided on using a static method and variable for this use. So something like this...
public class InitClass
{
static List PreloadedContent;
static ModelData GetContent(String ContentName)
{
//return the preloaded content that matches given name
}
}
The preloaded content may at some time decrease or increase in size depending on what the situation may call for. I've run into situations where something like this has been the only decent looking solution however; I think its an ugly solution.
Note: I can't load the data onto a class that needs it when it is created due to a variety of reasons - most of which are reasons I don't know about yet but will most likely come up. Certain classes will be loaded/unloaded depending on the rendering of the scene and my InitClass won't handle the creation of these objects most of the time.
Can anyone give me a better solution?
what you are doing is known as singleton. here are some previous discussions on this:
How to implement a singleton in C#
What’s a good threadsafe singleton generic template pattern in C#
To avoid static/global scope you could use some kind of Registry class. This means you have one class which you initialize at program startup. This class holds references to all other classes that need to be accessed globally.
Now you pass the initialized instance of your registry class to all instances in your application.
It isn't a very pretty soluation, but for me it is the best. With Static and global variables I always ended up in having some problems when testing or debugging code.
Another aproach would be to use a Singleton. Since they also just hold a static instance I would not prefer them.