Converting RValues.

src/renderer/parameters_context.rs

@@ -9,6 +9,41 @@ use crate::renderer::WalkError;
 use crate::renderer::Walkable;
 use std::collections::HashMap;
 
+/// Copy the data from an RValue to an Owned struct
+///
+/// In order to get comparisons to work for our `ContextElement` trait
+/// objects, we need to be able to use `std::any::Any`. Unfortunately,
+/// `Any` requires that the structs do not have a lifetime (so they
+/// will have a `'static` lifetime. This means that we cannot have a
+/// `<'a>` appended to the struct type, so the struct cannot contain
+/// any borrows. Rather than impose the copy cost in the parser, we
+/// are imposing the cost of copying the data in the renderer because
+/// the parser has no reason to not be able to reference data from the
+/// input string.
+pub enum OwnedRValue {
+    RVPath(OwnedPath),
+    RVString(String),
+}
+
+pub struct OwnedPath {
+    pub keys: Vec<String>,
+}
+
+impl From<RValue<'_>> for OwnedRValue {
+    fn from(original: RValue<'_>) -> Self {
+        match original {
+            RValue::RVString(text) => OwnedRValue::RVString(text.to_owned()),
+            RValue::RVPath(path) => OwnedRValue::RVPath(OwnedPath {
+                keys: path.keys.iter().map(|k| k.to_string()).collect(),
+            }),
+        }
+    }
+}
+
+pub struct NewParametersContext {
+    params: HashMap<String, OwnedRValue>,
+}
+
 #[derive(Clone, Debug)]
 pub struct ParametersContext<'a> {
     params: HashMap<&'a str, &'a RValue<'a>>,