Added function remove_value to HashMapContext

README.md

@@ -329,6 +329,10 @@ assert_eq!(eval_with_context_mut("a = 10; b = 1.0;", &mut context), Ok(().into()
 // ...and read the value in code like this
 assert_eq!(context.get_value("a"), Some(&Value::from_int(10)));
 assert_eq!(context.get_value("b"), Some(&Value::from_float(1.0)));
+// ...and remove the value in code like this
+assert_eq!(context.remove_value("a"), Ok(Some(Value::from_int(10))));
+// ...and if the value does not exist when removing, it returns None.
+assert_eq!(context.remove_value("a"), Ok(None));
 ```
 
 Contexts are also required for user-defined functions.

src/context/mod.rs

@@ -56,6 +56,14 @@ pub trait ContextWithMutableVariables: Context {
     ) -> EvalexprResult<(), Self::NumericTypes> {
         Err(EvalexprError::ContextNotMutable)
     }
+
+    /// Removes the variable with the given identifier from the context.
+    fn remove_value(
+        &mut self,
+        _identifier: &str,
+    ) -> EvalexprResult<Option<Value<Self::NumericTypes>>, Self::NumericTypes> {
+        Err(EvalexprError::ContextNotMutable)
+    }
 }
 
 /// A context that allows to assign to function identifiers.
@@ -352,6 +360,14 @@ impl<NumericTypes: EvalexprNumericTypes> ContextWithMutableVariables
         self.variables.insert(identifier, value);
         Ok(())
     }
+
+    fn remove_value(
+        &mut self,
+        identifier: &str,
+    ) -> EvalexprResult<Option<Value<Self::NumericTypes>>, Self::NumericTypes> {
+        // Removes a value from the `self.variables`, returning the value at the key if the key was previously in the map.
+        Ok(self.variables.remove(identifier))
+    }
 }
 
 impl<NumericTypes: EvalexprNumericTypes> ContextWithMutableFunctions

src/lib.rs

@@ -309,6 +309,10 @@
 //! // ...and read the value in code like this
 //! assert_eq!(context.get_value("a"), Some(&Value::from_int(10)));
 //! assert_eq!(context.get_value("b"), Some(&Value::from_float(1.0)));
+//! // ...and remove the value in code like this
+//! assert_eq!(context.remove_value("a"), Ok(Some(Value::from_int(10))));
+//! // ...and if the value does not exist when removing, it returns None.
+//! assert_eq!(context.remove_value("a"), Ok(None));
 //! ```
 //!
 //! Contexts are also required for user-defined functions.

tests/integration.rs

@@ -142,6 +142,16 @@ fn test_with_context() {
         eval_with_context("five < six && true", &context),
         Ok(Value::Boolean(true))
     );
+
+    assert_eq!(context.remove_value("half"), Ok(Some(Value::Float(0.5))));
+    assert_eq!(context.remove_value("zero"), Ok(Some(Value::Int(0))));
+    assert_eq!(context.remove_value("zero"), Ok(None));
+    assert_eq!(
+        eval_with_context("zero", &context),
+        Err(EvalexprError::VariableIdentifierNotFound(
+            "zero".to_string()
+        ))
+    );
 }
 
 #[test]