Why single inheritance??

[Sinex]

Hi,
Why does C# disallow multiple inheritance? Whats the reason behind this?
Is there any advantage or is it just a method to avoid some problems (if so,
what problems?) that come with multiple inheritance?

regards,
Sinex

[John Wood]

>> How is single inheritance with interfaces any different than multiple
inheritance where you only inherit 1 non-pure and many pure abstract bases ?
<<
Well er, it's basically the same. But that's not what people do when they're
talking about multiple inheritence, they're talking about multiple
implementation inheritence, not interface or abstract class.

Many people have suggested that this can be considerred good practice in multiple inheritance as well since it creates simpler sometimes more
flexible code (per bad design of default behaviors) and good programmers are
expensive. <<

Not sure how the 'and good programmers are expensive' bit links in to the
sentence but...
I agree that those times you want multiple inheritence should be a time to
step back and ask why you want it, and most of the time you end up realizing
that using interfaces and perhaps some aggregation (and encapsulation) is
actually a better solution.

Smalltalk offers multiple inheritence, but then again smalltalk lets you add
methods to existing objects, derive from primitive types and do all kinds of
weird things. It's basically a very liberal OOP language, which is nice n
all, but it comes with a huge performance penalty. And probably a huge
design penalty too.

--
John Wood
EMail: first name, dot, second name at priorganize.com
"Greg Young" <gr********@pla netbeach.com> wrote in message
news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..

ok everyone seems to have had their word ... Let me approach this
differently.

How is single inheritance with interfaces any different than multiple
inheritance where you only inherit 1 non-pure and many pure abstract bases ?
Many people have suggested that this can be considerred good practice in
multiple inheritance as well since it creates simpler sometimes more
flexible code (per bad design of default behaviors) and good programmers are expensive. The cost of the simpler code is the ability to provide default
behaviors in your many pure abstracts, if you are designing properly this
will probably not be a major issue.

Cheers,

Greg

"Sinex" <ma************ @honeywell.com> wrote in message
news:%2******** ********@TK2MSF TNGP12.phx.gbl. ..

Hi,
Why does C# disallow multiple inheritance? Whats the reason behind

this? Is there any advantage or is it just a method to avoid some problems (if

so,

what problems?) that come with multiple inheritance?

regards,
Sinex

[Simon Smith]

On 22 Jun 2004 16:20, "Greg Young" wrote:

ok everyone seems to have had their word ... Let me approach this
differently.

How is single inheritance with interfaces any different than multiple
inheritance where you only inherit 1 non-pure and many pure abstract bases ?

Many people have suggested that this can be considerred good practice in
multiple inheritance as well since it creates simpler sometimes more
flexible code (per bad design of default behaviors) and good programmers are
expensive. The cost of the simpler code is the ability to provide default
behaviors in your many pure abstracts, if you are designing properly this
will probably not be a major issue.

Cheers,

Greg

It's probably no different, I would have thought, and is pretty much exactly
what C#/.NET gives you.
But it is different to inheriting multiple non-pure abstract bases which
is the main point, I guess.
--
Simon Smith
simon dot s at ghytred dot com
http://www.ghytred.com/NewsLook - Usenet for Outlook

[Mickey Williams]

"John Wood" <sp**@isannoyin g.com> wrote in message
news:uy******** ******@TK2MSFTN GP11.phx.gbl...

I believe Eiffel supports multiple
inheritence this way also.

Eiffel implements multiple inheritance by creating shadow interfaces. The
CLR thinks that it's just single inheritance. Inside an Eiffel system, it
looks like MI, so you get the benefits of a language that supports MI
properly.

--
Mickey Williams
Author, "Microsoft Visual C# .NET Core Reference", MS Press
www.servergeek.com/blogs/mickey

[Reginald Blue]

Sinex wrote:

Why does C# disallow multiple inheritance? Whats the reason behind
this? Is there any advantage or is it just a method to avoid some
problems (if so, what problems?) that come with multiple inheritance?

Dreaded diamond pattern, for example:

http://www.parashift.com/c++-faq-lit....html#faq-25.8

Although a more comprehensive analysis of the tradeoffs for using multiple
inheritence and other techniques is in the previous FAQ:

http://www.parashift.com/c++-faq-lit....html#faq-25.6

Bottom line: Using MI correctly can be difficult, and the authors of C#
(and Java and more than a few other object languages, for that matter) felt
that it was safer to offer only single inheritance.

Of all the features missing from C#, multiple inheritance hasn't ever seemed
to be that big a deal to me...at least compared to things like
templates/generics (which eliminiates some of the needs for MI anyway.)

--
Reginald Blue
"I have always wished that my computer would be as easy to use as my
telephone. My wish has come true. I no longer know how to use my
telephone."
- Bjarne Stroustrup (originator of C++) [quoted at the 2003
International Conference on Intelligent User Interfaces]

[Michael Voss]

John Wood wrote:

Smalltalk offers multiple inheritence,
It doesn't (maybe except S#, which is a Smalltalk derivative that goes
beyond the Smalltalk specification in order to be able to use the CLR)...
but then again smalltalk lets you add
methods to existing objects,
Even at runtime, pretty cool ;-)
derive from primitive types
Smalltalk doesn't have something like a "primitive type", they are
completely normal classes that inherit from "Object", so you can derive from
them as they are nothing special like, say, in Java.
and do all kinds of weird things.
What do you consider "weird things" ?
It's basically a very liberal OOP language, which is nice n
all, but it comes with a huge performance penalty.
It's not that huge anymore. The executing speed with modern VM's comes very
close to Java and C#
And probably a huge design penalty too.

Could you elaborate on this ?

Cheers
Michael

[John Wood]

> > And probably a huge design penalty too.

Could you elaborate on this ?
Well 'huge' may be an exaggeration.

From experience I can say that liberal languages are easier to abuse. They
provide so many options, that usually in a moment of weakness the developer
chooses the easiest option, which isn't necessarily the best option.

A classic example is with C (and to a lesser extent C++), which let you do
pretty much anything with a pointer.

The comment stemmed from the thought that both MI, and the concept of adding
methods to existing objects, could easily be abused... and you could easily
end up with a terrible design built from 'easiest route' choices.

Just my opinion and a passing thought.

--
John Wood
EMail: first name, dot, second name at priorganize.com
"Michael Voss" <mi**********@l vrREMOVE.deCAPS > wrote in message
news:40d91efa$1 @news... John Wood wrote:

Smalltalk offers multiple inheritence,
It doesn't (maybe except S#, which is a Smalltalk derivative that goes
beyond the Smalltalk specification in order to be able to use the CLR)...

but then again smalltalk lets you add
methods to existing objects,

Even at runtime, pretty cool ;-)

derive from primitive types

Smalltalk doesn't have something like a "primitive type", they are
completely normal classes that inherit from "Object", so you can derive

from them as they are nothing special like, say, in Java.

and do all kinds of weird things.
What do you consider "weird things" ?

It's basically a very liberal OOP language, which is nice n
all, but it comes with a huge performance penalty.

It's not that huge anymore. The executing speed with modern VM's comes

very close to Java and C#

And probably a huge design penalty too.

Could you elaborate on this ?

Cheers
Michael