Add generic fmt::formatter for types with ToString(StringBuilderBase&)sb/reduce-allocs

Replace explicit fmt::formatter specializations for IoHash, Oid, and
Guid with a single concept-based generic formatter. Add ToString()
to IoHash as an inline delegate to ToHexString().

2 files changed, 15 insertions, 29 deletions

diff --git a/src/zencore/include/zencore/fmtutils.h b/src/zencore/include/zencore/fmtutils.h
index 2a829d2d5..a263c6f04 100644
--- a/src/zencore/include/zencore/fmtutils.h
+++ b/src/zencore/include/zencore/fmtutils.h
@@ -3,10 +3,7 @@
 #pragma once
 
 #include <zencore/filesystem.h>
-#include <zencore/guid.h>
-#include <zencore/iohash.h>
 #include <zencore/string.h>
-#include <zencore/uid.h>
 
 ZEN_THIRD_PARTY_INCLUDES_START
 #include <fmt/format.h>
@@ -60,39 +57,27 @@ struct fmt::formatter<T> : fmt::formatter<std::string_view>
 	}
 };
 
-template<>
-struct fmt::formatter<zen::IoHash> : formatter<string_view>
-{
-	template<typename FormatContext>
-	auto format(const zen::IoHash& Hash, FormatContext& ctx) const
-	{
-		zen::IoHash::String_t String;
-		Hash.ToHexString(String);
-		return fmt::formatter<string_view>::format({String, zen::IoHash::StringLength}, ctx);
-	}
-};
+// Generic formatter for any type with a ToString(StringBuilderBase&) member function.
+// This covers Guid, IoHash, Oid, and similar types without needing per-type
+// fmt::formatter specializations.
 
-template<>
-struct fmt::formatter<zen::Oid> : formatter<string_view>
+template<typename T>
+concept HasMemberToStringBuilder = std::is_class_v<T> && requires(const T& v, zen::StringBuilderBase& sb)
 {
-	template<typename FormatContext>
-	auto format(const zen::Oid& Id, FormatContext& ctx) const
 	{
-		zen::StringBuilder<32> String;
-		Id.ToString(String);
-		return fmt::formatter<string_view>::format({String.c_str(), zen::Oid::StringLength}, ctx);
-	}
-};
+		v.ToString(sb)
+		} -> std::same_as<zen::StringBuilderBase&>;
+} && !HasFreeToString<T> && !HasStringViewConversion<T>;
 
-template<>
-struct fmt::formatter<zen::Guid> : formatter<string_view>
+template<HasMemberToStringBuilder T>
+struct fmt::formatter<T> : fmt::formatter<std::string_view>
 {
 	template<typename FormatContext>
-	auto format(const zen::Guid& Id, FormatContext& ctx) const
+	auto format(const T& Value, FormatContext& ctx) const
 	{
-		zen::StringBuilder<48> String;
-		Id.ToString(String);
-		return fmt::formatter<string_view>::format({String.c_str(), zen::Guid::StringLength}, ctx);
+		zen::ExtendableStringBuilder<64> String;
+		Value.ToString(String);
+		return fmt::formatter<std::string_view>::format(String.ToView(), ctx);
 	}
 };
 
diff --git a/src/zencore/include/zencore/iohash.h b/src/zencore/include/zencore/iohash.h
index a619b0053..50c439b70 100644
--- a/src/zencore/include/zencore/iohash.h
+++ b/src/zencore/include/zencore/iohash.h
@@ -54,6 +54,7 @@ struct IoHash
 	static bool		   TryParse(std::string_view Str, IoHash& Hash);
 	const char*		   ToHexString(char* outString /* 40 characters + NUL terminator */) const;
 	StringBuilderBase& ToHexString(StringBuilderBase& outBuilder) const;
+	StringBuilderBase& ToString(StringBuilderBase& outBuilder) const { return ToHexString(outBuilder); }
 	std::string		   ToHexString() const;
 
 	static constexpr int StringLength = 40;