Re: [PATCH 3/7] [gdbsupport] Factor out base_next_iterator

[Tom de Vries <tdevries@suse.de>]

On 4/24/26 6:21 PM, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
> Tom> Instead, this patch factors out base_next_iterator, which contains all parts
> Tom> not specific to "next", in other words, everything except the operator++.
> 
> This looks pretty reasonable to me, though I wonder if it would be
> improved using the CRTP idiom.
> 
> It's not really needed but it could possibly be cleaner.
> 
> https://en.cppreference.com/cpp/language/crtp
> 

Thanks, I've done that in a v1 ( 
https://sourceware.org/pipermail/gdb-patches/2026-May/227066.html ).

> Tom> +   Instead of factoring out a base class, we could use something like this:
> Tom> +
> Tom> +     template<typename T, auto F = &T::next>
> Tom> +     struct next_iterator
> Tom> +     {
> Tom> +       ...
> Tom> +       self_type &operator++ ()
> Tom> +       {
> Tom> +	 m_item = m_item->*F;
> Tom> +	 return *this;
> Tom> +       }
> Tom> +       ...
> Tom> +     }
> Tom> +
> Tom> +  but that has the drawback that it doesn't work with incomplete T.  */
>   
> I am curious about this because I wonder how the current code could work
> with an incomplete T -- since the code references T::next directly.
> 
> Tom> -  explicit next_iterator (T *item)
> Tom> +  explicit base_next_iterator (T *item)
> Tom>      : m_item (item)
> Tom>    {
> Tom>    }
>   
> Tom>    /* Create a one-past-the-end iterator.  */
> Tom> -  next_iterator ()
> Tom> +  base_next_iterator ()
> Tom>      : m_item (nullptr)
> Tom>    {
> Tom>    }
> 
> These should probably be protected now because it doesn't make sense to
> directly instantiate a base_next_iterator.
> 

I did that initially, but Simon suggested importing the constructor from 
base_next_iterator, and that doesn't work if it's protected.


> Tom> +template<typename T>
> Tom> +struct next_iterator : base_next_iterator<T> {
> 
> Brace placement.
> 

Fixed.

> Tom> +  typedef next_iterator self_type;
> Tom> +  typedef T *value_type;
> Tom> +  typedef T *&reference;
> Tom> +  typedef T **pointer;
> 
> I would have thought most of these would be inherited.
> (I guess with CRTP this could all be in the base class)

That's indeed what happened, these are gone now.

Thanks,
- Tom