try using SFINAE instead of macro

Author: zhjwpku

src/iceberg/util/string_util.h

@@ -70,23 +70,26 @@ class ICEBERG_EXPORT StringUtils {
   }
 
   template <typename T>
-    requires std::is_arithmetic_v<T> && (!std::same_as<T, bool>)
+    requires std::is_integral_v<T> && (!std::same_as<T, bool>)
   static Result<T> ParseNumber(std::string_view str) {
-    T value = 0;
-    if constexpr (std::is_integral_v<T>) {
-      auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), value);
-      if (ec == std::errc() && ptr == str.data() + str.size()) [[likely]] {
-        return value;
-      }
-      if (ec == std::errc::result_out_of_range) {
-        return InvalidArgument("Failed to parse {} from string '{}': value out of range",
-                               typeid(T).name(), str);
-      }
-      return InvalidArgument("Failed to parse {} from string '{}': invalid argument",
+    T value{};
+    auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), value);
+    if (ec == std::errc() && ptr == str.data() + str.size()) [[likely]] {
+      return value;
+    }
+    if (ec == std::errc::result_out_of_range) {
+      return InvalidArgument("Failed to parse {} from string '{}': value out of range",
                              typeid(T).name(), str);
-    } else {
-// libc++ 20+ provides floating-point std::from_chars. Use fallback for older libc++
-#if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION >= 200000
+    }
+    return InvalidArgument("Failed to parse {} from string '{}': invalid argument",
+                           typeid(T).name(), str);
+  }
+
+  template <typename T>
+    requires std::is_floating_point_v<T>
+  static Result<T> ParseNumber(std::string_view str) {
+    T value{};
+    if constexpr (kHasFloatFromChars) {
       auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), value);
       if (ec == std::errc() && ptr == str.data() + str.size()) [[likely]] {
         return value;
@@ -97,7 +100,7 @@ class ICEBERG_EXPORT StringUtils {
       }
       return InvalidArgument("Failed to parse {} from string '{}': invalid argument",
                              typeid(T).name(), str);
-#else
+    } else {
       // strto* require null-terminated input; string_view does not guarantee it.
       std::string owned(str);
       const char* start = owned.c_str();
@@ -121,9 +124,17 @@ class ICEBERG_EXPORT StringUtils {
                                typeid(T).name(), str);
       }
       return value;
-#endif
     }
   }
+
+ private:
+  // libc++ 20+ provides floating-point std::from_chars; use strto* fallback for older
+  // versions.
+#if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION < 200000
+  static constexpr bool kHasFloatFromChars = false;
+#else
+  static constexpr bool kHasFloatFromChars = true;
+#endif
 };
 
 /// \brief Transparent hash function that supports std::string_view as lookup key