Merge pull request #60 from rstudio/inputs-readonly

Author: wch

shiny/reactive.py

@@ -44,8 +44,9 @@
 # Value
 # ==============================================================================
 class Value(Generic[T]):
-    def __init__(self, value: T) -> None:
+    def __init__(self, value: T, *, _read_only: bool = False) -> None:
         self._value: T = value
+        self._read_only: bool = _read_only
         self._dependents: Dependents = Dependents()
 
     # Calling the object is equivalent to `.get()`
@@ -58,6 +59,15 @@ def get(self) -> T:
         return self._value
 
     def set(self, value: T) -> bool:
+        if self._read_only:
+            raise RuntimeError(
+                "Can't set read-only reactive.Value. If you are trying to set an input value, use `update_xxx()` instead."
+            )
+        return self._set(value)
+
+    # The ._set() method allows setting read-only Value objects. This is used when the
+    # Value is part of a session.Inputs object, and the session wants to set it.
+    def _set(self, value: T) -> bool:
         if self._value is value:
             return False
 

shiny/session.py

@@ -238,7 +238,7 @@ def _manage_inputs(self, data: Dict[str, object]) -> None:
             if len(keys) == 2:
                 val = input_handlers.process_value(keys[1], val, keys[0], self)
 
-            self.input[keys[0]].set(val)
+            self.input[keys[0]]._set(val)
 
     # ==========================================================================
     # Message handlers
@@ -537,7 +537,7 @@ class Inputs:
     def __init__(self, **kwargs: object) -> None:
         self._map: dict[str, Value[Any]] = {}
         for key, value in kwargs.items():
-            self._map[key] = Value(value)
+            self._map[key] = Value(value, _read_only=True)
 
     def __setitem__(self, key: str, value: Value[Any]) -> None:
         if not isinstance(value, Value):
@@ -550,7 +550,7 @@ def __getitem__(self, key: str) -> Value[Any]:
         # dependencies on input values that haven't been received from client
         # yet.
         if key not in self._map:
-            self._map[key] = Value(None)
+            self._map[key] = Value(None, _read_only=True)
 
         return self._map[key]