Re: [PATCH v1 04/10] gdb support: add gdb::replace algorithm for iterators and ranges

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

On 10/07/2026 22:21, Kevin Buettner wrote:
> Hi Matthieu,
> 
> I am not a C++ expert, but I'd like to understand this better...
> 
> On Tue, 7 Jul 2026 16:48:54 +0100
> Matthieu Longo <matthieu.longo@arm.com> wrote:
> 
>> Add a gdb::replace helper that mirrors the behavior of std::replace
>> for iterator pairs, together with a convenience overload accepting a
>> range.
>>
>> This provides a C++17-compatible replacement for the C++20 std::replace/
>> std::ranges::replace algorithms, allowing callers to use a consistent
>> interface until GDB transitions to C++20. The helpers should be removed
>> once the C++ standard library implementations become available.
>> ---
>>  gdbsupport/array-view.h | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/gdbsupport/array-view.h b/gdbsupport/array-view.h
>> index 8431d7f5add..61119d7a8e2 100644
>> --- a/gdbsupport/array-view.h
>> +++ b/gdbsupport/array-view.h
>> @@ -225,6 +225,32 @@ void copy (gdb::array_view<U> src, gdb::array_view<T> dest)
>>      std::copy_backward (src.begin (), src.end (), dest.end ());
>>  }
>>  
>> +/* Replace all occurrences of a value in the provided range.
>> +
>> +   Note: this helper is a reimplementation of std::replace, only available
>> +   from C++20 onwards, and consequently, should be removed once we switch
>> +   to C++20.  */
>> +
>> +template <class ForwardIt, typename T>
>> +void replace (ForwardIt first, ForwardIt last,
>> +	      const T &old_value, const T &new_value)
>> +{
>> +  for (auto it = first; it != last; ++it)
>> +  {
>> +    if (*it == old_value)
>> +      *it = new_value;
>> +  }
>> +}
> 
> How does this differ from pre-C++20 std::replace?
> 
> Kevin
> 

I clearly misread the doc => https://en.cppreference.com/cpp/algorithm/replace

template< class ForwardIt, class T >
void replace( ForwardIt first, ForwardIt last,
              const T& old_value, const T& new_value );

	(1) 	(until C++26)
                (constexpr since C++20)

It was not added in C++20 but became constexpr since C++20.
Since the range version was added in C++20, I must have mixed it up in my head.

I removed this duplicate from the patch, and made the range version use std::replace instead.

commit 8854b859aec1a3cbcd3edeb571dc1388ac5b81f7
Author: Matthieu Longo <matthieu.longo@arm.com>
Date:   Fri Jul 3 16:02:13 2026 +0100

    gdb support: add gdb::ranges::replace algorithm

    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

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)
+{
+  std::replace (r.begin (), r.end (), old_value, new_value);
+}
+
+} /* namespace ranges */
+
 /* Compare LHS and RHS for (deep) equality.  That is, whether LHS and
    RHS have the same sizes, and whether each pair of elements of LHS
    and RHS at the same position compares equal.  */


Matthieu.