add back Ref.set_current

assignment expressions do not support attribute assignment

Author: rmorshea

docs/Dockerfile

@@ -1,6 +1,6 @@
 FROM python:3.8
 
-WORKDIR app/
+WORKDIR /app/
 
 # Install NodeJS
 # --------------

docs/source/examples/simple_dashboard.py

@@ -23,8 +23,18 @@ async def RandomWalk():
             .number-input-container input + input {margin-left: 4%}
             """
         ),
-        NumberInput("Mean", mu.current, mu.set, (-1, 1, 0.01)),
-        NumberInput("Standard Deviation", sigma.current, sigma.set, (0, 1, 0.01)),
+        NumberInput(
+            "Mean",
+            mu.current,
+            mu.set_current,
+            (-1, 1, 0.01),
+        ),
+        NumberInput(
+            "Standard Deviation",
+            sigma.current,
+            sigma.set_current,
+            (0, 1, 0.01),
+        ),
     )
 
 

idom/utils.py

@@ -3,10 +3,10 @@
 from typing import List, Tuple, Any, Dict, Callable, Optional, Generic, TypeVar
 
 
-_Current = TypeVar("_Current")
+_RefValue = TypeVar("_RefValue")
 
 
-class Ref(Generic[_Current]):
+class Ref(Generic[_RefValue]):
     """Hold a reference to a value
 
     This is used in imperative code to mutate the state of this object in order to
@@ -22,9 +22,18 @@ class Ref(Generic[_Current]):
 
     __slots__ = "current"
 
-    def __init__(self, initial_value: _Current) -> None:
+    def __init__(self, initial_value: _RefValue) -> None:
         self.current = initial_value
 
+    def set_current(self, new: _RefValue) -> _RefValue:
+        """Set the current value and return what is now the old value
+
+        This is nice to use in ``lambda`` functions.
+        """
+        old = self.current
+        self.current = new
+        return old
+
     def __eq__(self, other: Any) -> bool:
         return isinstance(other, Ref) and (other.current == self.current)
 

tests/test_utils.py

@@ -6,9 +6,14 @@
 
 def test_basic_ref_behavior():
     r = idom.Ref(1)
+    assert r.current == 1
+
     r.current = 2
     assert r.current == 2
 
+    assert r.set_current(3) == 2
+    assert r.current == 3
+
 
 def test_ref_equivalence():
     assert idom.Ref([1, 2, 3]) == idom.Ref([1, 2, 3])