Use std::visit with Visitor helper instead of std::holds_alternatve

include/file.hpp

@@ -21,14 +21,6 @@
 
 #include "gfx/main.hpp"
 
-// Convenience feature for visiting the below.
-template<typename... Ts>
-struct Visitor : Ts... {
-	using Ts::operator()...;
-};
-template<typename... Ts>
-Visitor(Ts...) -> Visitor<Ts...>;
-
 class File {
 	// Construct a `std::streambuf *` by default, since it's probably lighter than a `filebuf`.
 	std::variant<std::streambuf *, std::filebuf> _file;

include/helpers.hpp

@@ -85,4 +85,12 @@
 // For lack of <ranges>, this adds some more brevity
 #define RANGE(s) std::begin(s), std::end(s)
 
+// Convenience feature for visiting variants.
+template<typename... Ts>
+struct Visitor : Ts... {
+	using Ts::operator()...;
+};
+template<typename... Ts>
+Visitor(Ts...) -> Visitor<Ts...>;
+
 #endif // HELPERS_H