Return error when you try to change a global property. Fixes #71.

examples/births-deaths/infection_manager.rs

@@ -127,7 +127,9 @@ mod test {
 
         let mut context = Context::new();
 
-        context.set_global_property_value(Parameters, p_values.clone());
+        context
+            .set_global_property_value(Parameters, p_values.clone())
+            .unwrap();
         context.init_random(p_values.seed);
         init(&mut context);
 

examples/births-deaths/parameters_loader.rs

@@ -32,7 +32,9 @@ define_global_property!(Foi, HashMap<AgeGroupRisk, f64>);
 
 pub fn init_parameters(context: &mut Context, file_path: &Path) -> Result<(), IxaError> {
     let parameters_json = context.load_parameters_from_json::<ParametersValues>(file_path)?;
-    context.set_global_property_value(Parameters, parameters_json.clone());
+    context
+        .set_global_property_value(Parameters, parameters_json.clone())
+        .unwrap();
 
     let foi_map = parameters_json
         .foi_groups
@@ -41,7 +43,9 @@ pub fn init_parameters(context: &mut Context, file_path: &Path) -> Result<(), Ix
         .map(|x| (x.group_name, x.foi))
         .collect::<HashMap<AgeGroupRisk, f64>>();
 
-    context.set_global_property_value(Foi, foi_map.clone());
+    context
+        .set_global_property_value(Foi, foi_map.clone())
+        .unwrap();
 
     Ok(())
 }

examples/births-deaths/population_manager.rs

@@ -278,7 +278,9 @@ mod test {
         };
 
         let mut context = Context::new();
-        context.set_global_property_value(Parameters, p_values.clone());
+        context
+            .set_global_property_value(Parameters, p_values.clone())
+            .unwrap();
         context.init_random(p_values.seed);
 
         schedule_birth(&mut context);
@@ -300,7 +302,9 @@ mod test {
         };
 
         let mut context = Context::new();
-        context.set_global_property_value(Parameters, p_values.clone());
+        context
+            .set_global_property_value(Parameters, p_values.clone())
+            .unwrap();
         context.init_random(p_values.seed);
         let _person = context.create_new_person(0);
         schedule_death(&mut context);

examples/parameter-loading/infection_manager.rs

@@ -66,7 +66,9 @@ mod test {
         };
         let mut context = Context::new();
 
-        context.set_global_property_value(Parameters, p_values.clone());
+        context
+            .set_global_property_value(Parameters, p_values.clone())
+            .unwrap();
         context.init_random(42);
         init(&mut context);
 

examples/parameter-loading/parameters_loader.rs

@@ -21,6 +21,6 @@ define_global_property!(Parameters, ParametersValues);
 
 pub fn init_parameters(context: &mut Context, file_path: &Path) -> Result<(), IxaError> {
     let parameters_json = context.load_parameters_from_json::<ParametersValues>(file_path)?;
-    context.set_global_property_value(Parameters, parameters_json);
+    context.set_global_property_value(Parameters, parameters_json)?;
     Ok(())
 }

examples/parameter-loading/transmission_manager.rs

@@ -70,7 +70,9 @@ mod test {
         };
 
         let mut context = Context::new();
-        context.set_global_property_value(Parameters, p_values);
+        context
+            .set_global_property_value(Parameters, p_values)
+            .unwrap();
         context.init_random(123);
         let pid = context.add_person(()).unwrap();
         attempt_infection(&mut context);

examples/time-varying-infection/exposure_manager.rs

@@ -94,7 +94,9 @@ mod test {
             output_file: ".".to_string(),
         };
         let mut context = Context::new();
-        context.set_global_property_value(Parameters, p_values);
+        context
+            .set_global_property_value(Parameters, p_values)
+            .unwrap();
         let parameters = context
             .get_global_property_value(Parameters)
             .unwrap()
@@ -132,7 +134,9 @@ mod test {
             output_file: ".".to_string(),
         };
         let mut context = Context::new();
-        context.set_global_property_value(Parameters, p_values);
+        context
+            .set_global_property_value(Parameters, p_values)
+            .unwrap();
         let parameters = context
             .get_global_property_value(Parameters)
             .unwrap()

examples/time-varying-infection/infection_manager.rs

@@ -120,7 +120,9 @@ mod test {
         };
         let mut context = Context::new();
 
-        context.set_global_property_value(Parameters, p_values);
+        context
+            .set_global_property_value(Parameters, p_values)
+            .unwrap();
         let parameters = context
             .get_global_property_value(Parameters)
             .unwrap()
@@ -161,7 +163,9 @@ mod test {
             output_dir: ".".to_string(),
             output_file: ".".to_string(),
         };
-        context.set_global_property_value(Parameters, parameters.clone());
+        context
+            .set_global_property_value(Parameters, parameters.clone())
+            .unwrap();
         context.init_random(parameters.seed);
         for _ in 0..parameters.population {
             let person_id = context.add_person(()).unwrap();
@@ -211,7 +215,9 @@ mod test {
         let mut sum = 0.0;
         for seed in 0..n_iter {
             let mut context = Context::new();
-            context.set_global_property_value(Parameters, parameters.clone());
+            context
+                .set_global_property_value(Parameters, parameters.clone())
+                .unwrap();
             context.init_random(seed);
             init(&mut context);
             let person_id = context

examples/time-varying-infection/parameters_loader.rs

@@ -23,6 +23,6 @@ define_global_property!(Parameters, ParametersValues);
 
 pub fn init_parameters(context: &mut Context, file_path: &Path) -> Result<(), IxaError> {
     let parameters_json = context.load_parameters_from_json::<ParametersValues>(file_path)?;
-    context.set_global_property_value(Parameters, parameters_json);
+    context.set_global_property_value(Parameters, parameters_json)?;
     Ok(())
 }

src/error.rs

@@ -4,8 +4,8 @@ use std::io;
 
 #[derive(Debug)]
 #[allow(clippy::module_name_repetitions)]
-/// A wrapper around other error types, as well
-/// as our specific error type.
+/// Provides `IxaError` and maps to other errors to
+/// convert to an `IxaError`
 pub enum IxaError {
     IoError(io::Error),
     JsonError(serde_json::Error),

src/global_properties.rs

@@ -3,7 +3,7 @@ use crate::error::IxaError;
 use serde::de::DeserializeOwned;
 use std::any::{Any, TypeId};
 use std::cell::RefCell;
-use std::collections::HashMap;
+use std::collections::{hash_map::Entry, HashMap};
 use std::fmt::Debug;
 use std::fs;
 use std::io::BufReader;
@@ -40,7 +40,7 @@ where
                 if context.get_global_property_value(T::new()).is_some() {
                     return Err(IxaError::IxaError(format!("Duplicate property {name}")));
                 }
-                context.set_global_property_value(T::new(), val);
+                let _ = context.set_global_property_value(T::new(), val);
                 Ok(())
             },
         ),
@@ -122,11 +122,14 @@ crate::context::define_data_plugin!(
 
 pub trait ContextGlobalPropertiesExt {
     /// Set the value of a global property of type T
+    ///
+    /// # Errors
+    /// Will return an error if an attempt is made to change a value.
     fn set_global_property_value<T: GlobalProperty + 'static>(
         &mut self,
         property: T,
         value: T::Value,
-    );
+    ) -> Result<(), IxaError>;
 
     /// Return value of global property T
     fn get_global_property_value<T: GlobalProperty + 'static>(
@@ -171,11 +174,14 @@ impl GlobalPropertiesDataContainer {
         &mut self,
         _property: &T,
         value: T::Value,
-    ) {
-        let _data_container = self
-            .global_property_container
-            .entry(TypeId::of::<T>())
-            .or_insert_with(|| Box::new(value));
+    ) -> Result<(), IxaError> {
+        match self.global_property_container.entry(TypeId::of::<T>()) {
+            Entry::Vacant(entry) => {
+                entry.insert(Box::new(value));
+                Ok(())
+            }
+            Entry::Occupied(_) => Err(IxaError::from("Entry already exists")),
+        }
     }
 
     #[must_use]
@@ -194,9 +200,9 @@ impl ContextGlobalPropertiesExt for Context {
         &mut self,
         property: T,
         value: T::Value,
-    ) {
+    ) -> Result<(), IxaError> {
         let data_container = self.get_data_container_mut(GlobalPropertiesPlugin);
-        data_container.set_global_property_value(&property, value);
+        data_container.set_global_property_value(&property, value)
     }
 
     #[allow(unused_variables)]
@@ -252,16 +258,37 @@ mod test {
     }
 
     define_global_property!(DiseaseParams, ParamType);
-    //Since global properties aren't mutable right now, only
-    // check that they are properly set
+
     #[test]
     fn set_get_global_property() {
         let params: ParamType = ParamType {
             days: 10,
             diseases: 2,
         };
+        let params2: ParamType = ParamType {
+            days: 11,
+            diseases: 3,
+        };
+
         let mut context = Context::new();
-        context.set_global_property_value(DiseaseParams, params.clone());
+
+        // Set and check the stored value.
+        context
+            .set_global_property_value(DiseaseParams, params.clone())
+            .unwrap();
+        let global_params = context
+            .get_global_property_value(DiseaseParams)
+            .unwrap()
+            .clone();
+        assert_eq!(global_params.days, params.days);
+        assert_eq!(global_params.diseases, params.diseases);
+
+        // Setting again should fail because global properties are immutable.
+        assert!(context
+            .set_global_property_value(DiseaseParams, params2.clone())
+            .is_err());
+
+        // Check that the value is unchanged.
         let global_params = context
             .get_global_property_value(DiseaseParams)
             .unwrap()
@@ -298,7 +325,9 @@ mod test {
             .load_parameters_from_json::<ParamType>(&file_path)
             .unwrap();
 
-        context.set_global_property_value(Parameters, params_json);
+        context
+            .set_global_property_value(Parameters, params_json)
+            .unwrap();
 
         let params_read = context
             .get_global_property_value(Parameters)