order fixup

tip-of-the-week · Aug 13, 2023 · c4b4f33 · c4b4f33
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diff --git a/README.md b/README.md
@@ -16,8 +16,8 @@
 * [[342]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/342.md) - Did you know that C++26 added 'A nice placeholder with no name'?
 * [[341]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/341.md) - Did you know that C++26 added user-generated static_assert messages?
 * [[340]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/340.md) - Did you know that C++26 added bind front and back to NTTP callables?
-* [[339]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/339.md) - Did you know about C++20 `std::next_permutation` algorithm?
-* [[338]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/338.md) - Did you know that C++26 added `@, $, and `` to the basic character set?
+* [[339]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/339.md) - Did you know that C++26 added `@, $, and `` to the basic character set?
+* [[338]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/338.md) - Did you know about C++20 `std::next_permutation` algorithm?
 * [[337]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/337.md) - Did you know that run-time dispatching over type-list can be implemented many different ways?
 * [[336]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/336.md) - Did you know about `gnu::vector_size` extension?
 * [[335]](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/tips/335.md) - Did you know that you can simplify `boost.mp11` API with DSL?

diff --git a/tips/338.md b/tips/338.md
@@ -1,33 +1,176 @@
 <details open><summary>Info</summary><p>
 
-* **Did you know that C++26 added `@, $, and `` to the basic character set?**
+* **Did you know about C++20 `std::next_permutation` algorithm?**
 
-  * https://wg21.link/P2558R2
+  * https://eel.is/c++draft/alg.permutation.generators#lib:next_permutation
 
 </p></details><details open><summary>Example</summary><p>
 
 ```cpp
-auto $dollar_sign = 42;
-auto @commerical_at = 42;
-auto `grave_accent = 42;
+[[nodiscard]] constexpr auto factorial(const auto n) {
+    if (n == 0 or n == 1) {
+        return 1;
+    }
+    auto result = 1;
+    for (auto i = 2; i <= n; ++i) {
+        result *= i;
+    }
+    return result;
+}
+static_assert(1 == factorial(0));
+static_assert(1 == factorial(1));
+static_assert(1 * 2 == factorial(2));
+static_assert(1 * 2 * 3 == factorial(3));
+static_assert(1 * 2 * 3 * 4 == factorial(4));
+static_assert(1 * 2 * 3 * 4 * 5 == factorial(5));
+static_assert(1 * 2 * 3 * 4 * 5 * 6 == factorial(6));
 ```
 
+> https://godbolt.org/z/14r8EdevM
+
 </p></details><details open><summary>Puzzle</summary><p>
 
-* **Can you write code snippets where added characters can be used with added value?**
+* **Can you implement `permute invoke` which will try to call using all possible permutations?**
+
+```cpp
+// TODO invoke
+
+template <auto>
+struct Foo {};
+
+constexpr auto foo() { return 1; }
+constexpr auto bar(Foo<0>) { return 2; } constexpr auto baz(Foo<0>, Foo<1>) { return 3; }
+
+static_assert(1 == invoke<int>(foo));
+static_assert(2 == invoke<int>(bar, Foo<0>{}));
+static_assert(3 == invoke<int>(baz, Foo<0>{}, Foo<1>{}));
+static_assert(3 == invoke<int>(baz, Foo<1>{}, Foo<0>{}));
+```
+
+> https://godbolt.org/z/xeaxP46qW
 
 </p></details><details><summary>Solutions</summary><p>
 
 ```cpp
-// math
-auto a  = 42;
-auto a` = a*2;
+template <class T, auto N>
+[[nodiscard]] constexpr auto permute(std::array<T, N> nums) {
+    std::array<std::array<T, N>, factorial(N)> result{};
+    auto i = 0;
+    do {
+        result[i++] = nums;
+    } while (std::next_permutation(nums.begin(), nums.end()));
+    return result;
+}
+
+namespace detail {
+template<class> constexpr auto invoke(auto fn, auto... ts) -> std::pair<bool, decltype(fn(ts...))> { return {true, fn(ts...)}; }
+template<class R> constexpr auto invoke(...) -> std::pair<bool, R> { return {false, {}}; }
+
+template<auto N> constexpr auto nth(auto... args) {
+  return [&]<auto... Ns>(std::index_sequence<Ns...>) {
+    return [](decltype((void*)Ns)..., auto* nth, auto*...) {
+      return *nth;
+    }(&args...);
+  }
+  (std::make_index_sequence<N>{});
+}
+} // namespace detail
+
+template<class R>
+constexpr auto invoke(auto fn, auto... ts) -> R {
+    constexpr auto ids = []<auto... Ns>(std::index_sequence<Ns...>) { return std::array<std::size_t, sizeof...(Ns)>{Ns...}; }(std::make_index_sequence<sizeof...(ts)>{});
+    constexpr auto permutations = permute(ids);
+
+    R result;
+    bool called{};
+    [&]<auto... Ns>(std::index_sequence<Ns...>) {
+        ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
+            std::tie(called, result) = detail::invoke<R>(fn, detail::nth<permutations[N][Is]>(ts...)...);
+            return called;
+        }.template operator()<Ns>(std::make_index_sequence<permutations[Ns].size()>{}) or ...);
+    }(std::make_index_sequence<permutations.size()>{});
+    return result;
+}
+```
+
+> https://godbolt.org/z/vKbofePes
+
+```cpp
+template <class T, auto N>
+[[nodiscard]] constexpr auto permute(std::array<T, N> nums) {
+    std::array<std::array<T, N>, factorial(N)> result{};
+    auto i = 0;
+    do {
+        result[i++] = nums;
+    } while (std::next_permutation(nums.begin(), nums.end()));
+    return result;
+}
+
+namespace detail {
+template<class, auto N> constexpr auto invoke(auto fn, auto... ts) -> std::pair<std::integral_constant<int, N>, decltype(fn(ts...))> { return {{}, fn(ts...)}; }
+template<class R, auto> constexpr auto invoke(...) -> std::pair<std::integral_constant<int, 0>, R> { return {}; }
 
-// macros
-$macro(...) ```
+template<auto N> constexpr auto nth(auto... args) {
+  return [&]<auto... Ns>(std::index_sequence<Ns...>) {
+    return [](decltype((void*)Ns)..., auto* nth, auto*...) {
+      return *nth;
+    }(&args...);
+  }
+  (std::make_index_sequence<N>{});
+}
 
-// twitter
-auto id = @krisjusiak;
+template<class R, auto I, auto Size, auto Permutations, auto Split>
+constexpr auto invoke_impl(auto fn, auto... ts) -> R {
+    if constexpr (I >= Size) {
+        return {};
+    } else {
+        constexpr auto N = [&]<auto... Ns>(std::index_sequence<Ns...>) {
+            return ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
+                return decltype(detail::invoke<R, N+1>(fn, detail::nth<Permutations[N][Is]>(ts...)...)){}.first.value;
+            }.template operator()<I+Ns>(std::make_index_sequence<Permutations[I+Ns].size()>{}) + ...);
+        }(std::make_index_sequence<Split>{});
+
+        if constexpr (N > 0) {
+            constexpr auto N_ = N - 1;
+            return [&]<auto... Is>(std::index_sequence<Is...>) {
+                return detail::invoke<R, N_>(fn, detail::nth<Permutations[N_][Is]>(ts...)...).second;
+            }(std::make_index_sequence<Permutations[N_].size()>{});
+        } else {
+            constexpr auto chunks = Size / Split;
+            return invoke_impl<R, I+chunks, chunks, Permutations>(fn, ts...);
+        }
+    }
+}
+} // namespace detail
+
+template<class R>
+constexpr auto invoke(auto fn, auto... ts) -> R {
+    constexpr auto ids = []<auto... Ns>(std::index_sequence<Ns...>) { return std::array<std::size_t, sizeof...(Ns)>{Ns...}; }(std::make_index_sequence<sizeof...(ts)>{});
+    constexpr auto permutations = permute(ids);
+    constexpr auto max_params_without_chunking = 7;
+    constexpr auto split = 10;
+
+    if constexpr (sizeof...(ts) < max_params_without_chunking) {
+        constexpr auto N = [&]<auto... Ns>(std::index_sequence<Ns...>) {
+            return ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
+                return decltype(detail::invoke<R, N+1>(fn, detail::nth<permutations[N][Is]>(ts...)...)){}.first.value;
+            }.template operator()<Ns>(std::make_index_sequence<permutations[Ns].size()>{}) + ...);
+        }(std::make_index_sequence<permutations.size()>{});
+
+        if constexpr (N > 0) {
+            constexpr auto N_ = N - 1;
+            return [&]<auto... Is>(std::index_sequence<Is...>) {
+                return detail::invoke<R, N_>(fn, detail::nth<permutations[N_][Is]>(ts...)...).second;
+            }(std::make_index_sequence<permutations[N_].size()>{});
+        } else {
+            return {};
+        }
+    } else {
+      return detail::invoke_impl<R, 0, permutations.size(), permutations, split>(fn, ts...);
+    }
+}
 ```
 
+> https://godbolt.org/z/97ejzW4Px
+
 </p></details>
diff --git a/tips/339.md b/tips/339.md
@@ -1,176 +1,33 @@
 <details open><summary>Info</summary><p>
 
-* **Did you know about C++20 `std::next_permutation` algorithm?**
+* **Did you know that C++26 added `@, $, and `` to the basic character set?**
 
-  * https://eel.is/c++draft/alg.permutation.generators#lib:next_permutation
+  * https://wg21.link/P2558R2
 
 </p></details><details open><summary>Example</summary><p>
 
 ```cpp
-[[nodiscard]] constexpr auto factorial(const auto n) {
-    if (n == 0 or n == 1) {
-        return 1;
-    }
-    auto result = 1;
-    for (auto i = 2; i <= n; ++i) {
-        result *= i;
-    }
-    return result;
-}
-static_assert(1 == factorial(0));
-static_assert(1 == factorial(1));
-static_assert(1 * 2 == factorial(2));
-static_assert(1 * 2 * 3 == factorial(3));
-static_assert(1 * 2 * 3 * 4 == factorial(4));
-static_assert(1 * 2 * 3 * 4 * 5 == factorial(5));
-static_assert(1 * 2 * 3 * 4 * 5 * 6 == factorial(6));
+auto $dollar_sign = 42;
+auto @commerical_at = 42;
+auto `grave_accent = 42;
 ```
 
-> https://godbolt.org/z/14r8EdevM
-
 </p></details><details open><summary>Puzzle</summary><p>
 
-* **Can you implement `permute invoke` which will try to call using all possible permutations?**
-
-```cpp
-// TODO invoke
-
-template <auto>
-struct Foo {};
-
-constexpr auto foo() { return 1; }
-constexpr auto bar(Foo<0>) { return 2; } constexpr auto baz(Foo<0>, Foo<1>) { return 3; }
-
-static_assert(1 == invoke<int>(foo));
-static_assert(2 == invoke<int>(bar, Foo<0>{}));
-static_assert(3 == invoke<int>(baz, Foo<0>{}, Foo<1>{}));
-static_assert(3 == invoke<int>(baz, Foo<1>{}, Foo<0>{}));
-```
-
-> https://godbolt.org/z/xeaxP46qW
+* **Can you write code snippets where added characters can be used with added value?**
 
 </p></details><details><summary>Solutions</summary><p>
 
 ```cpp
-template <class T, auto N>
-[[nodiscard]] constexpr auto permute(std::array<T, N> nums) {
-    std::array<std::array<T, N>, factorial(N)> result{};
-    auto i = 0;
-    do {
-        result[i++] = nums;
-    } while (std::next_permutation(nums.begin(), nums.end()));
-    return result;
-}
-
-namespace detail {
-template<class> constexpr auto invoke(auto fn, auto... ts) -> std::pair<bool, decltype(fn(ts...))> { return {true, fn(ts...)}; }
-template<class R> constexpr auto invoke(...) -> std::pair<bool, R> { return {false, {}}; }
-
-template<auto N> constexpr auto nth(auto... args) {
-  return [&]<auto... Ns>(std::index_sequence<Ns...>) {
-    return [](decltype((void*)Ns)..., auto* nth, auto*...) {
-      return *nth;
-    }(&args...);
-  }
-  (std::make_index_sequence<N>{});
-}
-} // namespace detail
-
-template<class R>
-constexpr auto invoke(auto fn, auto... ts) -> R {
-    constexpr auto ids = []<auto... Ns>(std::index_sequence<Ns...>) { return std::array<std::size_t, sizeof...(Ns)>{Ns...}; }(std::make_index_sequence<sizeof...(ts)>{});
-    constexpr auto permutations = permute(ids);
-
-    R result;
-    bool called{};
-    [&]<auto... Ns>(std::index_sequence<Ns...>) {
-        ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
-            std::tie(called, result) = detail::invoke<R>(fn, detail::nth<permutations[N][Is]>(ts...)...);
-            return called;
-        }.template operator()<Ns>(std::make_index_sequence<permutations[Ns].size()>{}) or ...);
-    }(std::make_index_sequence<permutations.size()>{});
-    return result;
-}
-```
-
-> https://godbolt.org/z/vKbofePes
-
-```cpp
-template <class T, auto N>
-[[nodiscard]] constexpr auto permute(std::array<T, N> nums) {
-    std::array<std::array<T, N>, factorial(N)> result{};
-    auto i = 0;
-    do {
-        result[i++] = nums;
-    } while (std::next_permutation(nums.begin(), nums.end()));
-    return result;
-}
-
-namespace detail {
-template<class, auto N> constexpr auto invoke(auto fn, auto... ts) -> std::pair<std::integral_constant<int, N>, decltype(fn(ts...))> { return {{}, fn(ts...)}; }
-template<class R, auto> constexpr auto invoke(...) -> std::pair<std::integral_constant<int, 0>, R> { return {}; }
+// math
+auto a  = 42;
+auto a` = a*2;
 
-template<auto N> constexpr auto nth(auto... args) {
-  return [&]<auto... Ns>(std::index_sequence<Ns...>) {
-    return [](decltype((void*)Ns)..., auto* nth, auto*...) {
-      return *nth;
-    }(&args...);
-  }
-  (std::make_index_sequence<N>{});
-}
+// macros
+$macro(...) ```
 
-template<class R, auto I, auto Size, auto Permutations, auto Split>
-constexpr auto invoke_impl(auto fn, auto... ts) -> R {
-    if constexpr (I >= Size) {
-        return {};
-    } else {
-        constexpr auto N = [&]<auto... Ns>(std::index_sequence<Ns...>) {
-            return ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
-                return decltype(detail::invoke<R, N+1>(fn, detail::nth<Permutations[N][Is]>(ts...)...)){}.first.value;
-            }.template operator()<I+Ns>(std::make_index_sequence<Permutations[I+Ns].size()>{}) + ...);
-        }(std::make_index_sequence<Split>{});
-
-        if constexpr (N > 0) {
-            constexpr auto N_ = N - 1;
-            return [&]<auto... Is>(std::index_sequence<Is...>) {
-                return detail::invoke<R, N_>(fn, detail::nth<Permutations[N_][Is]>(ts...)...).second;
-            }(std::make_index_sequence<Permutations[N_].size()>{});
-        } else {
-            constexpr auto chunks = Size / Split;
-            return invoke_impl<R, I+chunks, chunks, Permutations>(fn, ts...);
-        }
-    }
-}
-} // namespace detail
-
-template<class R>
-constexpr auto invoke(auto fn, auto... ts) -> R {
-    constexpr auto ids = []<auto... Ns>(std::index_sequence<Ns...>) { return std::array<std::size_t, sizeof...(Ns)>{Ns...}; }(std::make_index_sequence<sizeof...(ts)>{});
-    constexpr auto permutations = permute(ids);
-    constexpr auto max_params_without_chunking = 7;
-    constexpr auto split = 10;
-
-    if constexpr (sizeof...(ts) < max_params_without_chunking) {
-        constexpr auto N = [&]<auto... Ns>(std::index_sequence<Ns...>) {
-            return ([&]<auto N, auto... Is>(std::index_sequence<Is...>) {
-                return decltype(detail::invoke<R, N+1>(fn, detail::nth<permutations[N][Is]>(ts...)...)){}.first.value;
-            }.template operator()<Ns>(std::make_index_sequence<permutations[Ns].size()>{}) + ...);
-        }(std::make_index_sequence<permutations.size()>{});
-
-        if constexpr (N > 0) {
-            constexpr auto N_ = N - 1;
-            return [&]<auto... Is>(std::index_sequence<Is...>) {
-                return detail::invoke<R, N_>(fn, detail::nth<permutations[N_][Is]>(ts...)...).second;
-            }(std::make_index_sequence<permutations[N_].size()>{});
-        } else {
-            return {};
-        }
-    } else {
-      return detail::invoke_impl<R, 0, permutations.size(), permutations, split>(fn, ts...);
-    }
-}
+// twitter
+auto id = @krisjusiak;
 ```
 
-> https://godbolt.org/z/97ejzW4Px
-
 </p></details>