From f7d4e445ffeaab8741f6518243d8a42b43749a91 Mon Sep 17 00:00:00 2001
From: Kyle Bowman <kyle+github@rocketbowman.com>
Date: Sun, 10 Mar 2024 11:38:36 -0400
Subject: [PATCH] Refactor: Single dispatch type-based argspecs.

---
 findings.md        |  9 +++++++++
 src/proto/utils.py | 35 +++++++++++++++++++++++++++--------
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/findings.md b/findings.md
index ef19191..0ca9873 100644
--- a/findings.md
+++ b/findings.md
@@ -57,6 +57,15 @@ if __name__ == "__main__":
 ## About Signatures
 * Argnames = Signature - Kwargs; this is a good way to report missing required arg
 
+## About Singledispatch
+
+* Use `@singledispatch` decorator to mark function`foo` a generic function.
+* Use `@foo.register` decorator to mark a function as an implemntation of `foo`.
+* Dispatch is based on the type of the first argument.
+* Method resolution is from specific to generic.
+* Use `foo.dispatch(<type>)` to determine which function is dispatched by `<type>`.
+* Use `foo.registry` to see all registered functions.
+
 # About MainCLI
 Purpose: 
 1. Search for other commands to register with it
diff --git a/src/proto/utils.py b/src/proto/utils.py
index 2116ea9..fe58b23 100644
--- a/src/proto/utils.py
+++ b/src/proto/utils.py
@@ -1,6 +1,9 @@
+import argparse
 from collections.abc import Callable
+from functools import singledispatch
 import inspect
-import argparse
+from typing import Union
+
 
 def get_defaults(fn: Callable)->tuple[list, dict]:
     """ Returns a dict of required arguments and a dict of kwarg defaults. """
@@ -57,13 +60,29 @@ def get_parser(fn: Callable)->argparse.ArgumentParser:
             argname = prm.name
 
         # NOTE: If you don't specify type in add_argument(), it will be parsed as a string.
-        # HACK: Whenever you see <class 'int'> you can use it as an initializer.
-        # It works consistently, but I haven't seen it as defined/supported behavior.
-        # Ex: type(42)('36') creates an integer 36.
-        if prm.annotation in (int, float, str):
-            arg_specs['type'] = prm.annotation
-        else:
-            pass
+        # Use get_argspecs() to add type-specific information to the arg_spec.
+        arg_specs | get_argspecs(prm.annotation(), arg_specs)
         
         parser.add_argument(argname, **arg_specs)
     return parser
+
+# NOTE: When a single dispatch function is invoked, the the first arg is inspected.
+# Based on the type of the first argument, a corresponding implementation is dispatched.
+# Use @foo.register to register an implementation to the single dispatch function foo.
+# The following two hacks are used throughout the get_argspecs implementations:
+# HACK: type(annotation) == type. But type(annotation()) == str | int | whatever. 
+# This hack works because of the following hack.
+# HACK: The 'type' type is callable. It behaves like a constructor for it's type.
+# For example: `type(42)('36')` creates an integer 36.
+# It works consistently, but I haven't seen it as defined/supported behavior.
+@singledispatch
+def get_argspecs(annotation: type, arg_specs: dict)->dict:
+    """ Creates a partial argspec dictionary from a parameter annotation. """
+    return arg_specs
+
+@get_argspecs.register
+def scalar_argspecs(annotation: Union[int, float, str], arg_specs)->dict:
+    """ Implements get_argspecs for integers, floats, and strings. """
+    arg_specs['type'] = type(annotation)
+    return arg_specs
+    
\ No newline at end of file
-- 
2.39.5