Return string instead of output pointer in metadata

[PragmaTwice]

-void ExtractNamespaceKey(Slice ns_key, std::string *ns, std::string *key, bool slot_id_encoded);
-void ComposeNamespaceKey(const Slice &ns, const Slice &key, std::string *ns_key, bool slot_id_encoded);
-void ComposeSlotKeyPrefix(const Slice &ns, int slotid, std::string *output);
+[[nodiscard]] std::tuple<Slice, Slice> ExtractNamespaceKey(Slice ns_key, bool slot_id_encoded);
+[[nodiscard]] std::string ComposeNamespaceKey(const Slice &ns, const Slice &key, bool slot_id_encoded);
+[[nodiscard]] std::string ComposeSlotKeyPrefix(const Slice &ns, int slotid);
 
 class InternalKey {
  public:
   ...
-  void Encode(std::string *out);
+  [[nodiscard]] std::string Encode() const;

[mapleFU]

The code LGTM, lets wait for CI and asan, since it might introduce memory problem...

[mapleFU]

So this is an optimization that return Slice rather than string?

[PragmaTwice]

Yeah, here it is unnecessary to return string. And if it is required, users can construct string manually from slice.

[torwig]

LGTM.

👍

[mapleFU]

LGTM, though it increase the risk of lifetine handling, the patch would improve our style(and make some string copy less)