c++: add any_of meta fn example

1 files changed, 22 insertions, 0 deletions

diff --git a/src/development/c++/meta3.cc b/src/development/c++/meta3.cc
new file mode 100644
index 0000000..5dce54a
--- /dev/null
+++ b/src/development/c++/meta3.cc
@@ -0,0 +1,22 @@
+// Copyright (C) 2022 johannst
+
+#include <type_traits>
+
+template<typename T, typename... U>
+struct any_of : std::false_type {};
+
+// Found our type T in the list of types U.
+template<typename T, typename... U>
+struct any_of<T, T, U...> : std::true_type {};
+
+// Pop off the first element in the list of types U,
+// since it didn't match our type T.
+template<typename T, typename U0, typename... U>
+struct any_of<T, U0, U...> : any_of<T, U...> {};
+
+// Convenience template variable to invoke meta function.
+template<typename T, typename... U>
+constexpr bool any_of_v = any_of<T, U...>::value;
+
+static_assert(any_of_v<int, char, bool, int>, "");
+static_assert(!any_of_v<int, char, bool, float>, "");