Re: [PATCH v2 2/6] gdb support: add gdb::ranges::replace algorithm

[Matthieu Longo <matthieu.longo@arm.com>]

On 10/09/2026 12:07, Andrew Burgess wrote:
> Matthieu Longo <matthieu.longo@arm.com> writes:
> 
>> Provide a C++17-compatible replacement for the C++20 std::ranges::replace
>> algorithm, allowing callers to use a consistent interface until GDB
>> transitions to C++20. The helper should be removed once the C++ standard
>> library implementation become available.
>>
>> https://en.cppreference.com/cpp/algorithm/ranges/replace
>> ---
>>  gdbsupport/array-view.h | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/gdbsupport/array-view.h b/gdbsupport/array-view.h
>> index 8431d7f5add..f9842ecff30 100644
>> --- a/gdbsupport/array-view.h
>> +++ b/gdbsupport/array-view.h
>> @@ -225,6 +225,22 @@ void copy (gdb::array_view<U> src, gdb::array_view<T> dest)
>>      std::copy_backward (src.begin (), src.end (), dest.end ());
>>  }
>>  
>> +namespace ranges {
>> +
>> +/* Replace all occurrences of a value in the provided range.
>> +
>> +   Note: this helper is a reimplementation of std::ranges::replace, only
>> +   available from C++20 onwards, and consequently, should be replaced by
>> +   std::ranges::replace once GDB switches to C++20.  */
>> +
>> +template <class Range, typename T>
>> +void replace (Range r, const T &old_value, const T &new_value)
> 
> Looking at the linked cppreference page, the C++20 functions take R as
> 'Range &&r'.  Doesn't your versions create a copy of the range?

Yes, it does.
Given that I was only using it gdb::array_view, I didn't notice the issue.
The replace cannot work with vectors as you pointed out below.

> This will work fine for non-owning ranges, like gdb::array_view, but will> mean replace operates
on a copy of the range for something like
> std::vector.  Even if what you have above is intentional, I think this
> difference should be highlighted and explained.
> 

I changed the function signature to use 'Range &&r'.

> Also, as this isn't specifically tied to gdb::array_view, I wonder if
> this would be better put into a new file gdbsupport/ranges.h ? I don't
> think anything much is needed to create the new file other than just
> adding the file, so that should be pretty easy to do.
>
> Thanks,
> Andrew

Done.

I also added:

#if __cplusplus >= 202002L
#error "replace the helpers below by the std::ranges::* equivalent."
#endif

in the file so that we don't forget about this and get rid of it once GDB migrates to C++20.
Is this ok ? Or to avoid ?

Matthieu