measurements: store to disk *after* evaluating them

i'm hoping to simplify a lot of serialization code with this

crates/coremem/src/meas.rs

@@ -15,7 +15,8 @@ pub trait AbstractMeasurement: Send + Sync + DynClone {
 }
 dyn_clone::clone_trait_object!(AbstractMeasurement);
 
-pub fn eval_multiple_kv(state: &dyn GenericSim, meas: &[Box<dyn AbstractMeasurement>]) -> IndexMap<String, String> {
+/// create one IndexMap out of several measurements
+pub fn eval_multiple_kv(state: &dyn GenericSim, meas: &[&dyn AbstractMeasurement]) -> IndexMap<String, String> {
     let mut r = IndexMap::new();
     for m in meas {
         let other = m.key_value(state);
@@ -24,6 +25,12 @@ pub fn eval_multiple_kv(state: &dyn GenericSim, meas: &[Box<dyn AbstractMeasurem
     r
 }
 
+pub fn eval_to_vec(state: &dyn GenericSim, meas: &[&dyn AbstractMeasurement]) -> Vec<Evaluated> {
+    eval_multiple_kv(state, meas).into_iter().map(|(k, v)| {
+        Evaluated::new(k, v)
+    }).collect()
+}
+
 #[derive(Clone, Serialize, Deserialize)]
 pub struct Time;
 
@@ -58,23 +65,26 @@ impl AbstractMeasurement for Meta {
     }
 }
 
+/// some measurement which has already been evaluated.
+/// this is used particularly if we need to monomorphize a measurement (e.g. for serialization)
+/// and know it won't be applied to a new/different state.
 #[derive(Clone, Serialize, Deserialize)]
-pub struct Label(pub String);
+pub struct Evaluated(String, String);
 
-impl Label {
-    pub fn new<S: Into<String>>(s: S) -> Self {
-        Self(s.into())
+impl Evaluated {
+    pub fn new<S1: Into<String>, S2: Into<String>>(key: S1, value: S2) -> Self {
+        Self(key.into(), value.into())
     }
 }
 
 #[typetag::serde]
-impl AbstractMeasurement for Label {
+impl AbstractMeasurement for Evaluated {
     fn eval(&self, _state: &dyn GenericSim) -> String {
-        self.0.clone()
+        self.1.clone()
     }
     fn key_value(&self, _state: &dyn GenericSim) -> IndexMap<String, String> {
         [
-            (self.0.clone(), self.0.clone()),
+            (self.0.clone(), self.1.clone()),
         ].into_iter().collect()
     }
 }