Thanks to encoding hooks, why not supporting arbitrary objects as dict keys? #568

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1. jcrist commented on Nov 7, 2023

   

   jcrist

   on Nov 7, 2023

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   Thanks for opening this; you've found a bug! This currently works correctly for msgspec.msgpack.decode and msgspec.convert, but fails for msgspec.json.decode. Will fix.
2. jcrist

   closed this as completedin #602on Dec 5, 2023
3. user529481 commented on Aug 14, 2024

   

   user529481

   on Aug 14, 2024

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   Hi @jcrist, I got a chance to look at the fix and the corresponding tests. I copied your test below and made Custom inherit msgspec.Struct. Encoding still works but now decoding throws the following error

   msgspec.ValidationError: Expected `object`, got `str` - at `key` in `$`
   

   This is the code I used to generate the error (taken from your tests)

   import msgspec
   from typing import Dict
   
   class Custom(msgspec.Struct):
       value : int
   
       def __hash__(self):
           return hash(self.value)
   
       def __eq__(self, other):
           return self.value == other.value
   
   def dec_hook(typ, obj):
       if typ == Custom:
           return Custom(obj)
       raise NotImplementedError
   
   msg = msgspec.json.encode(
       {Custom("a"): 1, Custom("b"): 2}, enc_hook=lambda x: x.value
   )
   assert msg == b'{"a":1,"b":2}'
   
   obj = msgspec.json.decode(msg, type=Dict[Custom, int], dec_hook=dec_hook)
   assert obj == {Custom("a"): 1, Custom("b"): 2}

   Is this expected behavior? Would it be difficult to support msgspec Structs as dictionary keys?