Add set_value to Scope.

README.md

@@ -733,12 +733,14 @@ fn main() -> Result<(), EvalAltResult>
     // First create the state
     let mut scope = Scope::new();
 
-    // Then push some initialized variables into the state
+    // Then push (i.e. add) some initialized variables into the state.
-    // NOTE: Remember the system number types in Rhai are i64 (i32 if 'only_i32') ond f64.
+    // Remember the system number types in Rhai are i64 (i32 if 'only_i32') ond f64.
     // Better stick to them or it gets hard working with the script.
     scope.push("y", 42_i64);
     scope.push("z", 999_i64);
-    scope.push("s", "hello, world!".to_string());   // remember to use 'String', not '&str'
+
+    // 'set_value' adds a variable when one doesn't exist
+    scope.set_value("s", "hello, world!".to_string());  // remember to use 'String', not '&str'
 
     // First invocation
     engine.eval_with_scope::<()>(&mut scope, r"
@@ -751,8 +753,12 @@ fn main() -> Result<(), EvalAltResult>
 
     println!("result: {}", result);                     // prints 979
 
-    // Variable y is changed in the script
+    // Variable y is changed in the script - read it with 'get_value'
-    assert_eq!(scope.get_value::<i64>("y").expect("variable x should exist"), 1);
+    assert_eq!(scope.get_value::<i64>("y").expect("variable y should exist"), 1);
+
+    // We can modify scope variables directly with 'set_value'
+    scope.set_value("y", 42_i64);
+    assert_eq!(scope.get_value::<i64>("y").expect("variable y should exist"), 42);
 
     Ok(())
 }

src/scope.rs

@@ -179,16 +179,44 @@ impl<'a> Scope<'a> {
     }
 
     /// Get the value of an entry in the Scope, starting from the last.
-    pub fn get_value<T: Any + Clone>(&self, key: &str) -> Option<T> {
+    pub fn get_value<T: Any + Clone>(&self, name: &str) -> Option<T> {
         self.0
             .iter()
             .enumerate()
             .rev() // Always search a Scope in reverse order
-            .find(|(_, Entry { name, .. })| name == key)
+            .find(|(_, Entry { name: key, .. })| name == key)
             .and_then(|(_, Entry { value, .. })| value.downcast_ref::<T>())
             .map(T::clone)
     }
 
+    /// Update the value of the named variable.
+    /// Search starts from the last, and only the last variable matching the specified name is updated.
+    /// If no variable matching the specified name is found, a new variable is added.
+    ///
+    /// # Panics
+    ///
+    /// Panics when trying to update the value of a constant.
+    pub fn set_value<T: Any + Clone>(&mut self, name: &'a str, value: T) {
+        match self.get(name) {
+            Some((
+                EntryRef {
+                    typ: EntryType::Constant,
+                    ..
+                },
+                _,
+            )) => panic!("variable {} is constant", name),
+            Some((
+                EntryRef {
+                    index,
+                    typ: EntryType::Normal,
+                    ..
+                },
+                _,
+            )) => self.0.get_mut(index).unwrap().value = value.into_dynamic(),
+            None => self.push(name, value.into_dynamic()),
+        }
+    }
+
     /// Get a mutable reference to an entry in the Scope.
     pub(crate) fn get_mut(&mut self, key: EntryRef) -> &mut Dynamic {
         let entry = self.0.get_mut(key.index).expect("invalid index in Scope");

tests/var_scope.rs

@@ -9,8 +9,12 @@ fn test_var_scope() -> Result<(), EvalAltResult> {
     assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "x")?, 9);
     engine.eval_with_scope::<()>(&mut scope, "x = x + 1; x = x + 2;")?;
     assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "x")?, 12);
+
+    scope.set_value("x", 42 as INT);
+    assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "x")?, 42);
+
     engine.eval_with_scope::<()>(&mut scope, "{let x = 3}")?;
-    assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "x")?, 12);
+    assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "x")?, 42);
 
     Ok(())
 }