Re: [PATCH kvm-unit-tests 2/4] Introduce a C++ wrapper for the kvm APIs

[Avi Kivity <avi@redhat.com>]

On 11/24/2010 07:27 PM, Anthony Liguori wrote:
>
> The alternative in C is:
>
> struct file_operations {
>    void (*release)(void);
>    void (*read)(...);
>    void (*write)(...);
> };
>
> struct file {
>   struct file_operations *ops;
> };
>
> If I do:
>
> static file_operations posix_file_ops = {
>   .read = posix_file_read,
>   .write = posix_file_write,
> };
>
> struct posix_file {
>   struct file parent;
>   int fd;
> };
>
> void posix_file_init(struct posix_file *obj)
> {
>     obj->parent.ops = posix_file_ops;
>     obj->fd = ...;
> };
>
> The compiler won't generate an error.  Only upon a call to 
> file_release() will a null pointer dereference happens whereas in C++, 
> because this paradigm is structured in the language, the compiler can 
> help assist you.

You forgot to mention:

   static void posix_file_read(struct file *_file, ...)
   {
        struct posix_file *file = container_of(_file, struct posix_file, 
parent);

        ...
   }

Even more boilerplate and potential for error.  But I think the worst 
thing about this is that it makes it hard to do the right thing, so 
people hack quick and dirty workarounds.  C++ makes this pattern trivial 
(if : laden), so people are encouraged to use it.

-- 
error compiling committee.c: too many arguments to function