From f5b21ea1581d8984f3c80b848302c9cd46307892 Mon Sep 17 00:00:00 2001
From: Gabriel de Marmiesse <gabrieldemarmiesse@gmail.com>
Date: Wed, 23 Aug 2023 22:43:17 +0200
Subject: [PATCH] Resolver is now immutable (#4)

---
 plum/function.py       |  7 +-----
 plum/resolver.py       | 29 +++++-------------------
 tests/test_resolver.py | 51 +++++++++++++++++-------------------------
 3 files changed, 27 insertions(+), 60 deletions(-)

diff --git a/plum/function.py b/plum/function.py
index a37a1030..ca82a8e4 100644
--- a/plum/function.py
+++ b/plum/function.py
@@ -134,8 +134,7 @@ def invalidate_resolver_and_cache(self):
     @property
     def resolver(self) -> Resolver:
         if self._resolver is None:
-            self._resolver = Resolver()
-            self._resolve_pending_registrations()
+            self._resolver = Resolver(self.get_all_subsignatures())
         return self._resolver
 
     @property
@@ -144,10 +143,6 @@ def cache(self) -> dict:
             self._cache = {}
         return self._cache
 
-    def _resolve_pending_registrations(self) -> None:
-        for subsignature in self.get_all_subsignatures():
-            self._resolver.register(subsignature)
-
     def get_all_subsignatures(self, strict: bool = True) -> Iterator[Signature]:
         # Perform any pending registrations.
         for f, signature, precedence in self._all_methods:
diff --git a/plum/resolver.py b/plum/resolver.py
index 66d1a97b..2d452544 100644
--- a/plum/resolver.py
+++ b/plum/resolver.py
@@ -1,4 +1,4 @@
-from typing import List, Tuple, Union
+from typing import Iterable, List, Tuple, Union
 
 from plum.signature import Signature
 
@@ -21,29 +21,10 @@ class Resolver:
         is_faithful (bool): Whether all signatures are faithful or not.
     """
 
-    def __init__(self):
-        self.signatures: List[Signature] = []
-        self.is_faithful: bool = True
-
-    def register(self, signature: Signature) -> None:
-        """Register a new signature.
-
-        Args:
-            signature (:class:`.signature.Signature`): Signature to add.
-        """
-        existing = [s == signature for s in self.signatures]
-        if any(existing):
-            if sum(existing) != 1:
-                raise AssertionError(
-                    f"The added signature `{signature}` is equal to {sum(existing)} "
-                    f"existing signatures. This should never happen."
-                )
-            self.signatures[existing.index(True)] = signature
-        else:
-            self.signatures.append(signature)
-
-        # Use a double negation for slightly better performance.
-        self.is_faithful = not any(not s.is_faithful for s in self.signatures)
+    def __init__(self, signatures: Iterable[Signature]):
+        signatures_dict = {hash(s): s for s in signatures}
+        self.signatures: List[Signature] = list(signatures_dict.values())
+        self.is_faithful: bool = all(s.is_faithful for s in self.signatures)
 
     def __len__(self) -> int:
         return len(self.signatures)
diff --git a/tests/test_resolver.py b/tests/test_resolver.py
index b622d972..53adbd91 100644
--- a/tests/test_resolver.py
+++ b/tests/test_resolver.py
@@ -7,46 +7,35 @@
 
 
 def test_initialisation():
-    r = Resolver()
+    r = Resolver([])
     # Without any registered signatures, the resolver should be faithful.
     assert r.is_faithful
 
 
 def test_register():
-    r = Resolver()
-
     # Test that faithfulness is tracked correctly.
-    r.register(Signature(int))
-    r.register(Signature(float))
+    r = Resolver([Signature(int), Signature(float)])
     assert r.is_faithful
-    r.register(Signature(Tuple[int]))
+    r = Resolver([Signature(int), Signature(float), Signature(Tuple[int])])
     assert not r.is_faithful
 
     # Test that signatures can be replaced.
-    new_s = Signature(float)
     assert len(r) == 3
+    new_s = Signature(float)
     assert r.signatures[1] is not new_s
-    r.register(new_s)
+    r = Resolver([Signature(int), Signature(float), Signature(Tuple[int]), new_s])
     assert len(r) == 3
     assert r.signatures[1] is new_s
 
-    # Test the edge case that should never happen.
-    r.signatures[2] = Signature(float)
-    with pytest.raises(
-        AssertionError,
-        match=r"(?i)the added signature `(.*)` is equal to 2 existing signatures",
-    ):
-        r.register(Signature(float))
-
 
 def test_len():
-    r = Resolver()
+    r = Resolver([])
     assert len(r) == 0
-    r.register(Signature(int))
+    r = Resolver([Signature(int)])
     assert len(r) == 1
-    r.register(Signature(float))
+    r = Resolver([Signature(int), Signature(float)])
     assert len(r) == 2
-    r.register(Signature(float))
+    r = Resolver([Signature(int), Signature(float), Signature(float)])
     assert len(r) == 2
 
 
@@ -80,16 +69,18 @@ class Missing:
     s_u = Signature(Unrelated)
     s_m = Signature(Missing)
 
-    r = Resolver()
-    r.register(s_b1)
-    # Import this after `s_b1` to test all branches.
-    r.register(s_a)
-    r.register(s_b2)
-    # Do not register `s_c1`.
-    r.register(s_c2)
-    r.register(s_u)
-    # Also do not register `s_m`.
-
+    r = Resolver(
+        [
+            s_b1,
+            # Import this after `s_b1` to test all branches.
+            s_a,
+            s_b2,
+            # Do not register `s_c1`.
+            s_c2,
+            s_u,
+            # Also do not register `s_m`.
+        ]
+    )
     # Resolve by signature.
     assert r.resolve(s_a) == s_a
     assert r.resolve(s_b1) == s_b1