Make Hugr covariant

CQCL · Aug 22, 2024 · 677ec36 · 677ec36
1 parent 9d3501f
commit 677ec36
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Showing 2 changed files with 8 additions and 6 deletions.
diff --git a/hugr-py/src/hugr/build/base.py b/hugr-py/src/hugr/build/base.py
@@ -2,16 +2,18 @@
 
 from __future__ import annotations
 
-from typing import (
-    Protocol,
-    cast,
-)
+from typing import TYPE_CHECKING, Protocol, TypeVar, cast
 
-from hugr.hugr.base import Hugr, OpVar
 from hugr.hugr.node_port import (
     Node,
     ToNode,
 )
+from hugr.ops import Op
+
+if TYPE_CHECKING:
+    from hugr.hugr.base import Hugr
+
+OpVar = TypeVar("OpVar", bound=Op)
 
 
 class ParentBuilder(ToNode, Protocol[OpVar]):

diff --git a/hugr-py/src/hugr/hugr/base.py b/hugr-py/src/hugr/hugr/base.py
@@ -62,7 +62,7 @@ def to_serial(self, node: Node) -> SerialOp:
 
 P = TypeVar("P", InPort, OutPort)
 K = TypeVar("K", InPort, OutPort)
-OpVar = TypeVar("OpVar", bound=Op)
+OpVar = TypeVar("OpVar", bound=Op, covariant=True)
 OpVar2 = TypeVar("OpVar2", bound=Op)