Multiple base classes in .NET

[Larry Smith]

I just read a blurb in MSDN under the C++ "ref" keyword which states that:

"Under the CLR object model, only public single inheritance is supported".

Does this mean that no .NET class can ever support multiple inheritance. In
C++ for instance I noticed that the compiler flags an error if you use the
"ref" keyword on a class with multiple base classes. This supports the above
quote. However, under the "CodeClass2.Bas es" property (part the VS
extensibility model), it states that:

"Bases are super types of CodeElements. For Visual Basic and Visual C#
there is always only one element in the collection except when the code type
is a CodeInterface".

This is true of course since these languages only support single (class)
inheritance. However, it should be true for all .NET classes based on the
first quote above. My issue is therefore this. I want to retrieve the base
class of an arbitrary class in an arbitrary code file by invoking
"CodeClass2.Bas es.Item(1)". This works in my testing but will it always work
for all languages in theory, assuming the class I'm targetting is always a
..NET class of course. Thanks in advance.

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

Larry Smith wrote:

I just read a blurb in MSDN under the C++ "ref" keyword which states that:

"Under the CLR object model, only public single inheritance is supported".

Does this mean that no .NET class can ever support multiple inheritance.

I belive so.

This is true of course since these languages only support single (class)
inheritance. However, it should be true for all .NET classes based on the
first quote above. My issue is therefore this. I want to retrieve the base
class of an arbitrary class in an arbitrary code file by invoking
"CodeClass2.Bas es.Item(1)". This works in my testing but will it always work
for all languages in theory, assuming the class I'm targetting is always a
.NET class of course. Thanks in advance.

If is is arbitrary code, then I belive that you should be using
Type BaseType.

And it is obvious that it will only return one type.

Arne

[Jesse Houwing]

* Larry Smith wrote, On 14-7-2007 1:49:

I just read a blurb in MSDN under the C++ "ref" keyword which states that:

"Under the CLR object model, only public single inheritance is supported".

Does this mean that no .NET class can ever support multiple inheritance. In
C++ for instance I noticed that the compiler flags an error if you use the
"ref" keyword on a class with multiple base classes. This supports the above
quote. However, under the "CodeClass2.Bas es" property (part the VS
extensibility model), it states that:

"Bases are super types of CodeElements. For Visual Basic and Visual C#
there is always only one element in the collection except when the code type
is a CodeInterface".

This is true of course since these languages only support single (class)
inheritance. However, it should be true for all .NET classes based on the
first quote above. My issue is therefore this. I want to retrieve the base
class of an arbitrary class in an arbitrary code file by invoking
"CodeClass2.Bas es.Item(1)". This works in my testing but will it always work
for all languages in theory, assuming the class I'm targetting is always a
.NET class of course. Thanks in advance.

The Visual Studio Extensibility model also supports non-CLR languages
(native C++ for example), so it has support for multiple inheritance.

The .NET types do not support multiple inheritance as you've already
found out. I've read a couple of rumors that multiple inheritance will
probably find its way back into the CLR in a future version...

Jesse

[Larry Smith]

>I just read a blurb in MSDN under the C++ "ref" keyword which states

>that:

"Under the CLR object model, only public single inheritance is
supported".

Does this mean that no .NET class can ever support multiple inheritance.

I belive so.

>This is true of course since these languages only support single (class)
inheritance. However, it should be true for all .NET classes based on the
first quote above. My issue is therefore this. I want to retrieve the
base class of an arbitrary class in an arbitrary code file by invoking
"CodeClass2.Ba ses.Item(1)". This works in my testing but will it always
work for all languages in theory, assuming the class I'm targetting is
always a .NET class of course. Thanks in advance.

If is is arbitrary code, then I belive that you should be using
Type BaseType.

Thanks for the tip. It might prove useful later but for the moment I might
not be able to retrieve the "Type" (since my app processes raw source files
before they may have even been compiled yet).

[Larry Smith]

The Visual Studio Extensibility model also supports non-CLR languages

(native C++ for example), so it has support for multiple inheritance.

The .NET types do not support multiple inheritance as you've already found
out. I've read a couple of rumors that multiple inheritance will probably
find its way back into the CLR in a future version...

Thanks for the clarification (appreciated). As for the rumour, I'm not sure
how they'll tackle that given that there already seem to be some built-in
assumptions based on single-inheritance. They could change this of course
but it might cause a lot of problems. Anyway, thanks again.

[Mark Rae [MVP]]

"Larry Smith" <no_spam@_nospa m.comwrote in message
news:eZ******** ******@TK2MSFTN GP05.phx.gbl...

Thanks for the clarification (appreciated). As for the rumour, I'm not
sure how they'll tackle that given that there already seem to be some
built-in assumptions based on single-inheritance. They could change this
of course but it might cause a lot of problems. Anyway, thanks again.

I'd be surprised if we ever see multiple inheritance in C#...

http://blogs.msdn.com/csharpfaq/arch.../07/85562.aspx
http://www.google.co.uk/search?hl=en...eritance&meta=
--
Mark Rae
ASP.NET MVP
http://www.markrae.net

[Larry Smith]

I'd be surprised if we ever see multiple inheritance in C#...

>
http://blogs.msdn.com/csharpfaq/arch.../07/85562.aspx
http://www.google.co.uk/search?hl=en...eritance&meta=

I'd be surpised as well. It's not likely to take off given that it's already
established as single inheritance. Moreover, it's rarely even used in the
C++ world. From my own (long) experience in that arena, it makes sense
conceptually but in practice it's mechanically very difficult to work with.
I doubt significant improvements can be made on this front.

[Mark Rae [MVP]]

"Larry Smith" <no_spam@_nospa m.comwrote in message
news:%2******** ********@TK2MSF TNGP03.phx.gbl. ..

I'd be surpised as well. It's not likely to take off given that it's
already established as single inheritance. Moreover, it's rarely even used
in the C++ world. From my own (long) experience in that arena, it makes
sense conceptually but in practice it's mechanically very difficult to
work with. I doubt significant improvements can be made on this front.

Indeed. I've been using C# since the latter half of 2002 and have never had
any need for multiple inheritance...
--
Mark Rae
ASP.NET MVP
http://www.markrae.net

[Peter Duniho]

(removed microsoft.publi c.vstudio.exten sibility and
microsoft.publi c.dotnet.framew ork.clr due to lack of relevance and
reduction of cross-posting)

On Sat, 14 Jul 2007 07:42:37 -0700, Larry Smith <no_spam@_nospa m.com>
wrote:

I'd be surpised as well. It's not likely to take off given that it's
already
established as single inheritance. Moreover, it's rarely even used in the
C++ world. From my own (long) experience in that arena, it makes sense
conceptually but in practice it's mechanically very difficult to work
with.
I doubt significant improvements can be made on this front.

IMHO, C# already does make an improvement over multiple inheritance vs
C++. That is, a class can in fact inherit multiple interfaces. This
allows for the same basic behavior as multiple inheritance, while forcing
the programmer to be explicit about how the class is arranged (ambiguity
in behavior of base classes shared by multiply inherited classes being one
of the bigger stumbling blocks for multiple inheritance in C++, IMHO).

Pete

[Paul Werkowitz]

Am Sat, 14 Jul 2007 16:37:06 +0100 schrieb Mark Rae [MVP]:

>
Indeed. I've been using C# since the latter half of 2002 and have never had
any need for multiple inheritance...

Hello, how then can you advise me to implement the following:

I have derivations from the standard WinForm Controls that implement
certain protocols for loading, storing, verification etc. Code example:

//-----------------------------------------------------------------
// boBindName
//
[
Bindable (true)
, Category ("QFC")
, Description ("Feld/Property, an das gebunden werden soll")
]
public string boBindName
{
get { return mBoBindName; }
set { mBoBindName = value; }
}

I have many of those.

At the moment, I need to have the exact same code in all of my derived
controls. Any change in that code must be manually repeated for all
controls - a perfect situation for implementation inheritance with the help
of MI.

Paule