From f6a687dc2b4c19dc1b3f6d9261e508bd6199daf1 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max.kellermann@gmail.com>
Date: Wed, 10 Jul 2024 22:04:34 +0200
Subject: [PATCH] util/FilteredContainer: new class
---
src/util/FilteredContainer.hxx | 116 +++++++++++++++++++++++++++++++++
1 file changed, 116 insertions(+)
create mode 100644 src/util/FilteredContainer.hxx
diff --git a/src/util/FilteredContainer.hxx b/src/util/FilteredContainer.hxx
new file mode 100644
index 000000000..6e2d8abfa
--- /dev/null
+++ b/src/util/FilteredContainer.hxx
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// author: Max Kellermann <max.kellermann@gmail.com>
+
+#pragma once
+
+#include <iterator> // for std::iterator_traits
+
+/**
+ * A container wrapper which returns only elements for which a second
+ * container returns true.
+ */
+template<std::input_iterator AB, typename AE,
+ std::input_iterator BB>
+class FilteredContainer {
+ [[no_unique_address]]
+ AB a_begin;
+
+ [[no_unique_address]]
+ AE a_end;
+
+ [[no_unique_address]]
+ BB b_begin;
+
+ struct end_iterator {
+ using Traits = std::iterator_traits<AE>;
+
+ using iterator_category = typename Traits::iterator_category;
+ using difference_type = typename Traits::difference_type;
+ using value_type = typename Traits::value_type;
+ using pointer = typename Traits::pointer;
+ using reference = typename Traits::reference;
+
+ AE a;
+ };
+
+public:
+ explicit constexpr FilteredContainer(AB _a_begin, AE _a_end, BB _b_begin) noexcept
+ :a_begin(_a_begin), a_end(_a_end), b_begin(_b_begin) {}
+
+ class iterator {
+ using Traits = std::iterator_traits<AB>;
+
+ [[no_unique_address]]
+ AB a;
+
+ [[no_unique_address]]
+ AE a_end;
+
+ [[no_unique_address]]
+ BB b;
+
+ public:
+ using iterator_category = typename std::forward_iterator_tag;
+ using difference_type = typename Traits::difference_type;
+ using value_type = typename Traits::value_type;
+ using pointer = typename Traits::pointer;
+ using reference = typename Traits::reference;
+
+ explicit constexpr iterator(AB _a, AE _a_end, BB _b) noexcept
+ :a(_a), a_end(_a_end), b(_b) {}
+
+ constexpr void FindEnabled() noexcept {
+ while (a != a_end && !*b) {
+ ++a;
+ ++b;
+ }
+ }
+
+ constexpr bool operator==(const iterator &other) const noexcept {
+ return a == other.a;
+ }
+
+ constexpr bool operator==(const end_iterator &other) const noexcept {
+ return a == other.a;
+ }
+
+ constexpr auto &operator++() noexcept {
+ ++a;
+ ++b;
+ FindEnabled();
+ return *this;
+ }
+
+ constexpr auto operator++(int) noexcept {
+ auto old = *this;
+ ++*this;
+ return old;
+ }
+
+ reference operator*() const noexcept {
+ return a.operator*();
+ }
+
+ pointer operator->() const noexcept {
+ return a.operator->();
+ }
+ };
+
+ constexpr iterator begin() const noexcept {
+ iterator it{a_begin, a_end, b_begin};
+ it.FindEnabled();
+ return it;
+ }
+
+ constexpr end_iterator end() const noexcept {
+ return {a_end};
+ }
+
+ constexpr iterator cbegin() const noexcept {
+ return begin();
+ }
+
+ constexpr end_iterator cend() const noexcept {
+ return end();
+ }
+};