computed_field: introspect return_type from annotation of wrapped method

[hottwaj]

Initial Checks

• I have searched Google & GitHub for similar requests and couldn't find anything
• I have read and followed the docs and still think this feature is missing

Description

Hi there, the "computed_field" decorator provides a return_type kwarg which allows the user to specify the expected return type of the wrapped function e.g.

@computed_field(return_type=int)
def get_score(self, data: Any):
    return 2000

I have a use case where defining and subsequently extracting the return type of a computed field is useful (in order to make our use of pydantic models more generic).

It seems though that setting return_type could be done more naturally by using a type annotation on the wrapped function? e.g. like this

@computed_field
def get_score(self, data: Any) -> int:
    return 2000

i.e. it would be great if computed_field or another internal part of pydantic can, if no "return_type" kwarg is provided, introspect the wrapped function to extract the return type annotation and use that as "return_type"

Affected Components

• Compatibility between releases
• Data validation/parsing
• Data serialization - .model_dump() and .model_dump_json()
• JSON Schema
• Dataclasses
• Model Config
• Field Types - adding or changing a particular data type
• Function validation decorator
• Generic Models
• Other Model behaviour - model_construct(), pickling, private attributes, ORM mode
• Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.