Why Multiple Inheritance not available in C#

Question

1.00/5 (1 vote)

See more:

ASP.NET

MVC

C#5.0

I want to know that why multiple inheritanc not implemented in C#.

Posted 17-Aug-15 22:05pm

Member 9129971

Add a Solution

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Peter Leow · Answer 1 · 2015-08-17T22:10:00

Solution 1

Check this out: http://www.programmerinterview.com/index.php/general-miscellaneous/why-dont-c-and-java-support-multiple-inheritance/[^]

Posted 17-Aug-15 22:10pm

Peter Leow

Comments

Member 9129971 18-Aug-15 5:22am

Thanks, a quite nice explanation but what is :: this character , here it shows that the D would get the copy through B, but i have not used this symbol yet in programming, so what this actually is and what its use is.
see here,
B :: testing = xTesting; // use B's version of testing

Peter Leow 18-Aug-15 9:06am

Although it rarely happens, the :: operator is used to resolve name conflicts between namespaces, classes, and members. In this case, it makes clear that it refers to the "testing" member of class B (not class C).

Member 9129971 18-Aug-15 9:56am

Thanks

Philippe Mori · Answer 2 · 2015-08-20T02:13:00

If you would have done a search you would have find a lot of answer on the web.

By the way, a similar question was already asked here on CodeProject and have more complete answers : Why C# does not support Multiple Inheritance ?[^]

Given that multiple inheritance is hard to implement and have majors impacts on the implementation of virtual tables and cast and that it was already well known that multiple inheritance cause a lot of problems, it is easy to understand why it was not supported in C#.

Although C++ support it, a lot of people would recommand to avoid using it (except from "interface"). Almost any time multiple inheritance could be used, it would be preferable to reconsider the design and use single inheritance and write wrapper fonctions that forward them to an internal object for function that would be available from an additionnal base class under multiple inheritance.

This will reduce coupling and it also allows to vary the type subobject which is not possible with multiple inheritance.

Also each potential feature has some potential benefits and also a potential of being used. In some cases, it only simplify code and in other it allows to solve completly new problems. Finally each feature can have potential problems too.

Thus choosing which feature make part of language is a decision between the PRO and CON of having it.

In the case of multiple inheritance, we have a lot of CONs:
- Hard to implement.
- Seldom used.
- High coupling.
- High maintenance cost.
- High chance of being misused.
- In most case, alternate solutions are better (for ex. composition and implementing multiple interfaces).
- Potential impact on the whole system performance (more complex code for cast and type system).
- Make the language more complex.
- Can affect all language that target to .NET.
- ...

F-ES Sitecore · Answer 3 · 2015-08-17T22:13:00

Solution 2

Virtual methods are too complex to properly implement.

Posted 17-Aug-15 22:13pm

F-ES Sitecore

Comments

Member 9129971 18-Aug-15 5:24am

so you mean ,complexity is the only reason for this, does it has something to do with the .net framework?
Since it not implemented in any .net language

F-ES Sitecore 18-Aug-15 6:07am

Yes it is the .net framework more than individual language implementations. They just decided to not implement it as handling virtual methods when a class inherits from two other classes is a tricky issue.

Philippe Mori 18-Aug-15 12:30pm

The complexity is mainly from a maintenance perspective by abusing of it. It is far better to uses interfaces and not rely on inheritance too much for code sharing...

F-ES Sitecore 19-Aug-15 4:13am

You have to use the right tool for the job. If that is interfaces then use them, if it is inheritance then use that. You can rarely substitute one for the other as one comes with implementation and one does not.

Philippe Mori 19-Aug-15 8:49am

And there is the problem... You want to reuse part of the implementation even though it is not a is-a relationship... Well private or protected inheritance can then be used but somewhere down the path class hierarchy could change and then it affect all those classes.

A design that avoid multiple inheritance is almost always a better option. If one need to reuse code then it can make some helper classes instead of inheriting code. Less coupling is better for maintenance.
Given the complexity of multiple inheritance and the fact that generally avoiding it lead to better design and the fact that from C++ experience, it was known to cause as much problems as it solve, it is easy to understand why it was not supported. If it was supported, then any language targetting .NET would have to support it...

F-ES Sitecore 19-Aug-15 9:04am

The possibility to abuse something or to implement bad design based on something isn't going to stop MS creating it as a language feature. People will always abuse things and badly architect things, it isn't something for the vendor to try and control. MS have gone on record as saying that virtual methods are the main reason multiple inheritance is not supported.

Philippe Mori 19-Aug-15 10:04am

One of the purpose of C# was to be simpler to implement and use. Another one was to be safer than C++ by avoiding construct that were known to be error-prone.

Not supporting multiple inheritance make perfect sense in that context.

For a compiler writer, they have no interest to implement a feature that is complex to implement properly, that is seldom used and was already known to cause more problem than it solve.

F-ES Sitecore 19-Aug-15 11:38am

The only thing stopping multiple inheritance from being "safe" and less complex to implement properly are virtual methods.

Philippe Mori 19-Aug-15 12:18pm

Diamond shape related issues also add complexity to the language even without virtual functions. And it is even worst with virtual bases (shared base classes).

Also, base qualifier is then not enough to call base method or constructor as you would need a way to explicitly specify which one.

Also C# only support public inheritance which also contribute to make the language simpler...

Thus there are a few important issues that make it complex to implement and use.

F-ES Sitecore 19-Aug-15 12:33pm

For sure it adds some complexity, but so does covariance and contravariance with generics, but we still have them. As I said though, MS have gone on record as saying that virtual methods were the main reason multi inheritance was not implemented in .net.

Philippe Mori 20-Aug-15 8:32am

Although the complexity of virtual methods might be the main reason, I think that those decision are a balance between benefits and costs. See my answer.