The plus plus

[Andy Green]

Alan Cox wrote:

Hi Alan -

>> guy.  Somehow the kernel and Gnome reached a local optimum at the C 
>> hacker level and that is where they stay.
> 
> The kernel uses C for good sound reasons - C++ is slower, harder to

Well C++ can generate pure C with no overhead, in the degenerate case 
you are not using the C++ features.  So it is not "slower" without some 
qualification.

About ten years ago when I was struggling to understand what the C++ 
deal was about, I realized after it crashed in on me what the benefits 
were (the moment I understood how virtual functions worked in the memory 
footprint) that I had been blindly reaching for some of the same 
principles in my C for some time, eg, binding related data into structs, 
composing structs with other more primitive structs at the start, making 
the equivalent of constructor functions to prep a struct, using function 
pointers and so on.

When I look at bits of the kernel code I need to understand to write my 
drivers, I strongly recognize the same aping of OO principles in a 
pre-OO language.  The shared mindmeld that produced such code is ripe to 
move on IMO!

Since for the kernel there is an attempt at implementing the OO action 
in C by hand at the moment, it is even harder to flat out say that C++ 
is "slower" without qualification, since it by delivering implicitly 
what is done explicitly now it offsets at least some of the overhead.

> debug and the tools suck in relative terms. You can use a subset of C++
> to write OS core code, that has been demonstrated, but C++ is not
> beneficial in that space. Much of that is down to the fact C++ is a
> dreadfully designed language rather than going agains the basic argument
> about using the right tools for the right job. 

Well I think a lot of your skills, experience and opinion, in fact only 
illness kept me from the last Linux World where I was anxious to hear 
your security talk.  But you only need to buy into a pretty thin subset 
of C++ to get the bulk of the benefit IMO.  You don't need any of that 
">>" operator trickery or to use string.

> From the kernel viewpoint C++ is the badly designed swiss army knife
> bought in a cheap junk shop - it has lots of interesting ways to cut
> yourself but none of the tools actually help you do anything useful.

For sure there is a lot that a wise person avoids, particularly in the 
libs and templates, but the core class stuff only delivers wins IMO. 
Just use it as a better C compiler that natively supports the 
abstractions you already insisted to use, you don't have to buy into 
anything else.

The original context was the relative success of a C++-based GUI and a 
C-based one.  Concepts like pure virtual classes give really strong 
architectural structure to the implementation, a newbie can glance at 
the class definitions and keenly understand the whole deal in a 
hierarchical, complete and contained way.  Deep structure is readably 
captured by the class definitions and derivations.

Before I blew out of being a Windows Trained Monkey I wrote a lot of MFC 
for UI, there is much to like in having UI elements integrated into an 
OO language, this experience gives me the assurance to claim that C++ 
makes a major difference in the consistency and architecture you can 
hope to succeed with.

-Andy