msgspec · jcrist · Feb 1, 2023 · Jan 31, 2023 · Feb 1, 2023 · Feb 1, 2023
diff --git a/docs/source/api.rst b/docs/source/api.rst
@@ -133,6 +133,7 @@ Inspect
 .. autoclass:: TimeType
 .. autoclass:: DateType
 .. autoclass:: UUIDType
+.. autoclass:: DecimalType
 .. autoclass:: ExtType
 .. autoclass:: RawType
 .. autoclass:: EnumType

diff --git a/docs/source/extending.rst b/docs/source/extending.rst
@@ -65,39 +65,38 @@ by defining two callback functions:
 - ``dec_hook`` in ``Decoder``, for converting natively supported types back
   into a custom type when using :ref:`typed decoding <typed-decoding>`.
 
-Here we define ``enc_hook`` and ``dec_hook`` callbacks to convert
-`decimal.Decimal` objects to/from strings, which are then natively handled by
-``msgspec``.
+Here we define ``enc_hook`` and ``dec_hook`` callbacks to convert `complex`
+objects to/from objects, which are then natively handled by ``msgspec``.
 
 .. code-block:: python
 
     import msgspec
     from typing import Any, Type
-    from decimal import Decimal
 
     def enc_hook(obj: Any) -> Any:
-        if isinstance(obj, Decimal):
-            # convert the Decimal to a str
-            return str(obj)
+        if isinstance(obj, complex):
+            # convert the complex to a tuple of real, imag
+            return (obj.real, obj.imag)
         else:
             # Raise a TypeError for other types
             raise TypeError(f"Objects of type {type(obj)} are not supported")
 
 
     def dec_hook(type: Type, obj: Any) -> Any:
         # `type` here is the value of the custom type annotation being decoded.
-        if type is Decimal:
-            # Convert ``obj`` (which should be a ``str``) to a Decimal
-            return Decimal(obj)
+        if type is complex:
+            # Convert ``obj`` (which should be a ``tuple``) to a complex
+            real, imag = obj
+            return complex(real, imag)
         else:
             # Raise a TypeError for other types
             raise TypeError(f"Objects of type {type} are not supported")
 
 
-    # Define a message that contains a Decimal
+    # Define a message that contains a complex type
     class MyMessage(msgspec.Struct):
         field_1: str
-        field_2: Decimal
+        field_2: complex
 
     # Create an encoder and a decoder using the custom callbacks.
     # Note that typed deserialization is required for successful
@@ -106,10 +105,7 @@ Here we define ``enc_hook`` and ``dec_hook`` callbacks to convert
     dec = msgspec.json.Decoder(MyMessage, dec_hook=dec_hook)
 
     # An example message
-    msg = MyMessage(
-        "some string",
-        Decimal("3.1415926535897932384626433832795"),
-    )
+    msg = MyMessage("some string", complex(1, 2))
 
     # Encode and decode the message to show that things work
     buf = enc.encode(msg)

diff --git a/docs/source/supported-types.rst b/docs/source/supported-types.rst
@@ -20,6 +20,7 @@ Most combinations of the following types are supported (with a few restrictions)
 - `datetime.date`
 - `datetime.time`
 - `uuid.UUID`
+- `decimal.Decimal`
 - `typing.Any`
 - `typing.Optional`
 - `typing.Union`
@@ -317,6 +318,31 @@ timezone-naive by specifying a ``tz`` constraint (see
         File "<stdin>", line 1, in <module>
     msgspec.ValidationError: Invalid UUID
 
+``decimal``
+-----------
+
+`decimal.Decimal` values are serialized as their string representation in all
+protocols. This ensures no precision loss during serialization, as would happen
+with a float representation.
+
+.. code-block:: python
+
+    >>> import decimal
+
+    >>> x = decimal.Decimal("1.2345")
+
+    >>> msg = msgspec.json.encode(x)
+
+    >>> msg
+    b'"1.2345"'
+
+    >>> msgspec.json.decode(msg, type=decimal.Decimal)
+    Decimal('1.2345')
+
+    >>> msgspec.json.decode(b'"oops"', type=decimal.Decimal)
+    Traceback (most recent call last):
+        File "<stdin>", line 1, in <module>
+    msgspec.ValidationError: Invalid decimal string
 
 ``list`` / ``tuple`` / ``set`` / ``frozenset``
 ----------------------------------------------
@@ -714,9 +740,9 @@ Union restrictions are as follows:
 
 - Unions may contain at most one type that encodes to a string (`str`,
   `enum.Enum`, `bytes`, `bytearray`, `datetime.datetime`, `datetime.date`,
-  `datetime.time`, `uuid.UUID`). Note that this restriction is fixable with
-  some work, if this is a feature you need please `open an issue
-  <https://github.com/jcrist/msgspec/issues>`__.
+  `datetime.time`, `uuid.UUID`, `decimal.Decimal`). Note that this restriction
+  is fixable with some work, if this is a feature you need please `open an
+  issue <https://github.com/jcrist/msgspec/issues>`__.
 
 - Unions may contain at most one type that encodes to an object (`dict`,
   `typing.TypedDict`, `dataclasses.dataclass`, `Struct` with