xo-flatstring: + README + docs + test coverage

include/xo/flatstring/string_view_concat.hpp

@@ -0,0 +1,30 @@
+#include <string_view>
+#include <array>
+
+template <std::string_view const & ... Strings>
+struct sv_concat
+{
+    static constexpr auto impl() noexcept {
+        constexpr std::size_t n = (Strings.size() + ... + 0);
+
+        std::array<char, n + 1> arr{};
+
+        auto append = [i=0, &arr](const auto & s) mutable {
+            for (auto c : s)
+                arr[i++] = c;
+        };
+        (append(Strings), ...);
+        arr[n] = '\0';
+
+        return arr;
+    }
+
+    static constexpr auto arr = impl();
+    static constexpr std::string_view value {
+        arr.data(),
+        arr.size() - 1
+    };
+};
+
+template <std::string_view const & ... Strings>
+static constexpr auto concat_v = sv_concat<Strings...>::value;