From 42361a924d924daa315866df2ebbc7ea69727125 Mon Sep 17 00:00:00 2001
From: Nana Sakisaka <1901813+saki7@users.noreply.github.com>
Date: Sun, 6 Sep 2026 11:57:28 +0900
Subject: [PATCH] Improve `run_length_sequence` interface

---
 include/iris/error/throwf.hpp        |   5 +-
 include/iris/error/throwf_format.hpp |   8 +--
 include/iris/run_length_sequence.hpp | 100 +++++++++++++++++++++++++++
 3 files changed, 107 insertions(+), 6 deletions(-)

diff --git a/include/iris/error/throwf.hpp b/include/iris/error/throwf.hpp
index eac5e0c..7eb18d3 100644
--- a/include/iris/error/throwf.hpp
+++ b/include/iris/error/throwf.hpp
@@ -24,11 +24,12 @@ inline namespace error_functions {
 // critical paths as some compilers fail to optimize the plain `throw` statement
 // even though the statement itself should imply `[[noreturn]]`.
 template<class E>
+    requires std::is_default_constructible_v<E>
 IRIS_CONFIG_THROW_NORETURN void throwf()
 {
     static_assert(std::is_base_of_v<std::exception, E>);
     static_assert(std::is_constructible_v<E>);
-    IRIS_CONFIG_THROW_IMPL(E{});
+    IRIS_CONFIG_THROW_IMPL(E());
 }
 
 // This function can be used to strongly assume optimization in some performance-
@@ -40,7 +41,7 @@ IRIS_CONFIG_THROW_NORETURN void throwf(Arg&& arg, Rest&&... rest)
 {
     static_assert(std::is_base_of_v<std::exception, E>);
     static_assert(!std::is_base_of_v<std::exception, std::remove_cvref_t<Arg>>, "don't copy/move construct exception types directly");
-    IRIS_CONFIG_THROW_IMPL(E{std::forward<Arg>(arg), std::forward<Rest>(rest)...});
+    IRIS_CONFIG_THROW_IMPL(E(std::forward<Arg>(arg), std::forward<Rest>(rest)...));
 }
 
 } // error_functions
diff --git a/include/iris/error/throwf_format.hpp b/include/iris/error/throwf_format.hpp
index 0403227..2235833 100644
--- a/include/iris/error/throwf_format.hpp
+++ b/include/iris/error/throwf_format.hpp
@@ -33,7 +33,7 @@ template<class E, class... Args>
 IRIS_CONFIG_THROW_NORETURN void throwf(std::format_string<Args...> fmt, Args&&... args)
 {
     static_assert(std::is_base_of_v<std::exception, E>);
-    IRIS_CONFIG_THROW_IMPL(E{std::format(std::move(fmt), std::forward<Args>(args)...)});
+    IRIS_CONFIG_THROW_IMPL(E(std::format(std::move(fmt), std::forward<Args>(args)...)));
 }
 
 template<class E, NotStringLike Arg0, class... Args>
@@ -41,7 +41,7 @@ template<class E, NotStringLike Arg0, class... Args>
 IRIS_CONFIG_THROW_NORETURN void throwf(Arg0&& arg0, std::format_string<Args...> fmt, Args&&... args)
 {
     static_assert(std::is_base_of_v<std::exception, E>);
-    IRIS_CONFIG_THROW_IMPL(E{std::forward<Arg0>(arg0), std::format(std::move(fmt), std::forward<Args>(args)...)});
+    IRIS_CONFIG_THROW_IMPL(E(std::forward<Arg0>(arg0), std::format(std::move(fmt), std::forward<Args>(args)...)));
 }
 
 template<class E, NotStringLike Arg0, NotStringLike Arg1, class... Args>
@@ -50,10 +50,10 @@ IRIS_CONFIG_THROW_NORETURN void throwf(Arg0&& arg0, Arg1&& arg1, std::format_str
 {
     static_assert(std::is_base_of_v<std::exception, E>);
     IRIS_CONFIG_THROW_IMPL(
-        E{
+        E(
             std::forward<Arg0>(arg0), std::forward<Arg1>(arg1),
             std::format(std::move(fmt), std::forward<Args>(args)...)
-        }
+        )
     );
 }
 
diff --git a/include/iris/run_length_sequence.hpp b/include/iris/run_length_sequence.hpp
index 3ee71c2..4eb3be1 100644
--- a/include/iris/run_length_sequence.hpp
+++ b/include/iris/run_length_sequence.hpp
@@ -15,6 +15,7 @@
 #include <iris/requirements.hpp>
 #include <iris/type_traits.hpp>
 
+#include <functional>
 #include <algorithm>
 #include <vector>
 #include <ranges>
@@ -145,6 +146,23 @@ class run_length_sequence
             return {index(), *value_it_};
         }
 
+        [[nodiscard]] constexpr T const& run_value() const noexcept
+        {
+            return *value_it_;
+        }
+
+        constexpr void advance_run() noexcept
+        {
+            ++ofs_it_;
+            ++value_it_;
+            rel_pos_ = static_cast<IndexT>(0u);
+        }
+        [[nodiscard]] friend constexpr iterator_impl next_run(iterator_impl it) noexcept
+        {
+            it.advance_run();
+            return it;
+        }
+
         constexpr iterator_impl& operator++() noexcept
         {
             auto ofs_next = std::next(ofs_it_);
@@ -469,6 +487,88 @@ class run_length_sequence
         );
     }
 
+    template<class Pred>
+        requires std::predicate<Pred&, T const&>
+    [[nodiscard]] constexpr const_iterator find_run_if(const_iterator from, Pred&& pred) const
+        noexcept(std::is_nothrow_invocable_v<Pred&, T const&>)
+    {
+        auto const last = this->end();
+        for (; from != last; from.advance_run()) {
+            if (std::invoke(pred, from.run_value())) {
+                return from;
+            }
+        }
+        return last;
+    }
+
+    template<class Pred>
+        requires std::predicate<Pred&, T const&>
+    [[nodiscard]] constexpr const_iterator find_run_if_not(const_iterator from, Pred&& pred) const
+        noexcept(std::is_nothrow_invocable_v<Pred&, T const&>)
+    {
+        auto const last = this->end();
+        for (; from != last; from.advance_run()) {
+            if (!std::invoke(pred, from.run_value())) {
+                return from;
+            }
+        }
+        return last;
+    }
+
+    template<class U>
+        requires req::half_equality_comparable<T, U>
+    [[nodiscard]] constexpr const_iterator find_run(const_iterator from, U const& value) const
+        noexcept(noexcept(std::declval<T const&>() == value))
+    {
+        return this->find_run_if(std::move(from), [&](T const& e) noexcept(noexcept(e == value)) {
+            return e == value;
+        });
+    }
+
+    template<class U>
+        requires req::half_equality_comparable<T, U>
+    [[nodiscard]] constexpr const_iterator find_run_not(const_iterator from, U const& value) const
+        noexcept(noexcept(std::declval<T const&>() != value))
+    {
+        return this->find_run_if(std::move(from), [&](T const& e) noexcept(noexcept(e != value)) {
+            return e != value;
+        });
+    }
+
+    // ---------------------------------------------------------------------
+
+    template<class Pred>
+        requires std::predicate<Pred&, T const&>
+    [[nodiscard]] constexpr const_iterator find_run_if(Pred&& pred) const
+        noexcept(noexcept(this->find_run_if(begin(), std::forward<Pred>(pred))))
+    {
+        return this->find_run_if(begin(), std::forward<Pred>(pred));
+    }
+
+    template<class Pred>
+        requires std::predicate<Pred&, T const&>
+    [[nodiscard]] constexpr const_iterator find_run_if_not(Pred&& pred) const
+        noexcept(noexcept(this->find_run_if_not(begin(), std::forward<Pred>(pred))))
+    {
+        return this->find_run_if_not(begin(), std::forward<Pred>(pred));
+    }
+
+    template<class U>
+        requires req::half_equality_comparable<T, U>
+    [[nodiscard]] constexpr const_iterator find_run(U const& value) const
+        noexcept(noexcept(this->find_run(begin(), value)))
+    {
+        return this->find_run(begin(), value);
+    }
+
+    template<class U>
+        requires req::half_equality_comparable<T, U>
+    [[nodiscard]] constexpr const_iterator find_run_not(U const& value) const
+        noexcept(noexcept(this->find_run_not(begin(), value)))
+    {
+        return this->find_run_not(begin(), value);
+    }
+
     // ---------------------------------------------------------------------
 
     // Returns an iterator to the element at logical position `pos`, or `end()`