Add example: filter_int_iterator.cpp

examples/CMakeLists.txt

@@ -4,7 +4,7 @@
 # cmake-format: on
 
 # List of all buildable examples.
-set(EXAMPLES repeated_chars_iterator)
+set(EXAMPLES filter_int_iterator repeated_chars_iterator)
 
 foreach(example ${EXAMPLES})
   # Add example executable.

examples/filter_int_iterator.cpp

@@ -0,0 +1,69 @@
+// examples/filter_int_iterator.cpp -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// P2727R4 example: An iterator that allows filtering int elements of a sequence.
+#include <beman/iterator_interface/iterator_interface.hpp>
+
+#include <algorithm>
+#include <array>
+#include <iostream>
+
+// filtered_int_iterator uses std::iterator_interface to define a forward iterator
+// that iterates over a sequence of integers, skipping those that do not satisfy a predicate.
+template <typename Pred>
+struct filtered_int_iterator
+    : beman::iterator_interface::ext_iterator_interface_compat<filtered_int_iterator<Pred>,
+                                                               std::forward_iterator_tag,
+                                                               int> {
+    // Default constructor creates an end-of-range iterator.
+    filtered_int_iterator() : m_it_begin(nullptr) {}
+
+    // Constructor for the beginning of the sequence.
+    filtered_int_iterator(int* it_begin, int* it_end, Pred pred) : m_it_begin(it_begin), m_it_end(it_end), m_pred(std::move(pred)) {
+        m_it_begin = std::find_if(m_it_begin, m_it_end, m_pred);
+    }
+
+    // A forward iterator based on iterator_interface usually requires
+    // three user-defined operations.  since we are adapting an existing
+    // iterator (an int *), we only need to define this one.  The others are
+    // implemented by iterator_interface, using the underlying int *.
+    filtered_int_iterator& operator++() {
+        m_it_begin = std::find_if(std::next(m_it_begin), m_it_end, m_pred);
+        return *this;
+    }
+
+    // It is really common for iterator adaptors to have a base() member
+    // function that returns the adapted iterator.
+    int* base() const { return m_it_begin; }
+
+  private:
+    // Provide access to base_reference.
+    friend beman::iterator_interface::iterator_interface_access;
+
+    // Provide access to base_reference.
+    constexpr auto base_reference() noexcept { return m_it_begin; }
+
+    // Start of the sequence of integers.
+    int* m_it_begin;
+
+    // End of the sequence of integers.
+    int* m_it_end;
+
+    // Predicate that determines which integers to skip.
+    Pred m_pred;
+};
+
+int main() {
+    // Create a filtered_int_iterator that iterates over the sequence {1, 2, 3, 4, 10, 11, 101, 200, 0}, skipping odd numbers.
+    // 0 is not skipped, so it will be the last element in the sequence.
+    std::array a = {1, 2, 3, 4, 10, 11, 101, 200, 0};
+    filtered_int_iterator it{std::begin(a), std::end(a), [](int i) { return i % 2 == 0; }};
+
+    while (*it) {
+        std::cout << *it << " ";
+        ++it;
+    }
+    std::cout << "\n";
+
+    return 0;
+}

examples/repeated_chars_iterator.cpp

@@ -20,7 +20,7 @@ class repeated_chars_iterator
     // Default constructor creates an end-of-range iterator.
     constexpr repeated_chars_iterator() : m_it_begin(nullptr), m_fixed_size(0), m_pos(0) {}
 
-    // Constructor for the beginning of the range.
+    // Constructor for the beginning of the sequence.
     constexpr repeated_chars_iterator(const char* it_begin, difference_type size, difference_type n)
         : m_it_begin(it_begin), m_fixed_size(size), m_pos(n) {}