Add format_string

Author: geier1993

src/eckit/format/Format.h

@@ -41,14 +41,17 @@
 
 namespace eckit {
 
+template<typename ...T>
+using format_string = fmt::format_string<T...>;
+
 /// Format a string with compile time checks.
 /// @param formatString to use, see: <https://fmt.dev/11.1/syntax/> for description of syntax.
 ///        Must be known at compiletime
 /// @param ... args to be upplied into formatString
 /// @throws fmt::format_error
-template <typename StringType, typename... Args>
-std::string format(StringType&& formatString, Args&&... args) {
-    return fmt::format(fmt::runtime(std::forward<StringType>(formatString)), std::forward<Args>(args)...);
+template <typename... Args>
+std::string format(format_string<Args...> formatString, Args&&... args) {
+    return fmt::format(fmt::runtime(std::move(formatString)), std::forward<Args>(args)...);
 }
 
 
@@ -58,9 +61,9 @@ std::string format(StringType&& formatString, Args&&... args) {
 ///        Must be known at compiletime
 /// @param ... args to be upplied into formatString
 /// @throws fmt::format_error
-template <typename OutputIt, typename StringType, typename... Args, std::enable_if_t<!std::is_base_of_v<std::ostream, std::decay_t<OutputIt>>, bool> = true>
-void format_to(OutputIt&& outputIt, StringType&& formatString, Args&&... args) {
-    fmt::format_to(std::forward<OutputIt>(outputIt), fmt::runtime(std::forward<StringType>(formatString)), std::forward<Args>(args)...);
+template <typename OutputIt, typename... Args, std::enable_if_t<!std::is_base_of_v<std::ostream, std::decay_t<OutputIt>>, bool> = true>
+void format_to(OutputIt&& outputIt, format_string<Args...> formatString, Args&&... args) {
+    fmt::format_to(std::forward<OutputIt>(outputIt), fmt::runtime(std::move(formatString)), std::forward<Args>(args)...);
 }
 
 /// Format a string with compile time checks to an ostream
@@ -69,10 +72,10 @@ void format_to(OutputIt&& outputIt, StringType&& formatString, Args&&... args) {
 ///        Must be known at compiletime
 /// @param ... args to be upplied into formatString
 /// @throws fmt::format_error
-template <typename StringType, typename... Args>
-void format_to(std::ostream& os, StringType&& formatString, Args&&... args) {
+template <typename... Args>
+void format_to(std::ostream& os, format_string<Args...> formatString, Args&&... args) {
     // Have to either use `const char&` or `const wchar_t&` here 
-    fmt::format_to(std::ostream_iterator<const char&>(os), fmt::runtime(std::forward<StringType>(formatString)), std::forward<Args>(args)...);
+    fmt::format_to(std::ostream_iterator<const char&>(os), fmt::runtime(std::move(formatString)), std::forward<Args>(args)...);
 }