diff --git a/src/ast.rs b/src/ast.rs
index 140a7cd8..ecac8042 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -618,9 +618,9 @@ pub enum Stmt {
     /// `for` id `in` expr `{` stmt `}`
     For(Expr, Box<(String, Stmt)>, Position),
     /// \[`export`\] `let` id `=` expr
-    Let(Box<Ident>, Option<Expr>, bool, Position),
+    Let(Box<IdentX>, Option<Expr>, bool, Position),
     /// \[`export`\] `const` id `=` expr
-    Const(Box<Ident>, Option<Expr>, bool, Position),
+    Const(Box<IdentX>, Option<Expr>, bool, Position),
     /// expr op`=` expr
     Assignment(Box<(Expr, Cow<'static, str>, Expr)>, Position),
     /// `{` stmt`;` ... `}`
diff --git a/src/engine.rs b/src/engine.rs
index 129ff1cf..b053af40 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -2302,9 +2302,9 @@ impl Engine {
                 };
                 let (var_name, _alias): (Cow<'_, str>, _) = if state.is_global() {
                     (
-                        var_def.name.clone().into(),
+                        var_def.name.to_string().into(),
                         if *export {
-                            Some(var_def.name.to_string())
+                            Some(var_def.name.clone())
                         } else {
                             None
                         },
@@ -2371,7 +2371,7 @@ impl Engine {
                     // Mark scope variables as public
                     if let Some(index) = scope.get_index(name).map(|(i, _)| i) {
                         let alias = rename.as_ref().map(|x| &x.name).unwrap_or_else(|| name);
-                        scope.add_entry_alias(index, alias.to_string());
+                        scope.add_entry_alias(index, alias.clone());
                     } else {
                         return EvalAltResult::ErrorVariableNotFound(name.to_string(), *id_pos)
                             .into();
diff --git a/src/module/mod.rs b/src/module/mod.rs
index 510c0884..6db9889d 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -120,9 +120,9 @@ impl FuncInfo {
 #[derive(Clone)]
 pub struct Module {
     /// Sub-modules.
-    modules: HashMap<String, Shared<Module>>,
+    modules: HashMap<ImmutableString, Shared<Module>>,
     /// Module variables.
-    variables: HashMap<String, Dynamic>,
+    variables: HashMap<ImmutableString, Dynamic>,
     /// Flattened collection of all module variables, including those in sub-modules.
     all_variables: HashMap<u64, Dynamic, StraightHasherBuilder>,
     /// External Rust functions.
@@ -160,7 +160,7 @@ impl fmt::Debug for Module {
             "Module(\n    modules: {}\n    vars: {}\n    functions: {}\n)",
             self.modules
                 .keys()
-                .map(String::as_str)
+                .map(|m| m.as_str())
                 .collect::<Vec<_>>()
                 .join(", "),
             self.variables
@@ -331,7 +331,11 @@ impl Module {
     /// assert_eq!(module.get_var_value::<i64>("answer").unwrap(), 42);
     /// ```
     #[inline(always)]
-    pub fn set_var(&mut self, name: impl Into<String>, value: impl Variant + Clone) -> &mut Self {
+    pub fn set_var(
+        &mut self,
+        name: impl Into<ImmutableString>,
+        value: impl Variant + Clone,
+    ) -> &mut Self {
         self.variables.insert(name.into(), Dynamic::from(value));
         self.indexed = false;
         self
@@ -458,7 +462,7 @@ impl Module {
     #[inline(always)]
     pub fn set_sub_module(
         &mut self,
-        name: impl Into<String>,
+        name: impl Into<ImmutableString>,
         sub_module: impl Into<Shared<Module>>,
     ) -> &mut Self {
         self.modules.insert(name.into(), sub_module.into());
@@ -1423,7 +1427,7 @@ impl Module {
         other.modules.iter().for_each(|(k, v)| {
             let mut m = Self::new();
             m.merge_filtered(v, _filter);
-            self.set_sub_module(k, m);
+            self.set_sub_module(k.clone(), m);
         });
         #[cfg(feature = "no_function")]
         self.modules
diff --git a/src/parser.rs b/src/parser.rs
index 34c4f848..479c2778 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -826,7 +826,7 @@ fn parse_switch(
         }
     }
 
-    let mut table = HashMap::with_capacity_and_hasher(16, StraightHasherBuilder);
+    let mut table = HashMap::new();
     let mut def_stmt = None;
 
     loop {
@@ -915,9 +915,12 @@ fn parse_switch(
         }
     }
 
+    let mut final_table = HashMap::with_capacity_and_hasher(table.len(), StraightHasherBuilder);
+    final_table.extend(table.into_iter());
+
     Ok(Stmt::Switch(
         item,
-        Box::new((table, def_stmt)),
+        Box::new((final_table, def_stmt)),
         settings.pos,
     ))
 }
@@ -2158,14 +2161,14 @@ fn parse_let(
         AccessMode::ReadWrite => {
             let var_name = state.get_interned_string(name.clone());
             state.stack.push((var_name, AccessMode::ReadWrite));
-            let var_def = Ident::new(name, pos);
+            let var_def = IdentX::new(name, pos);
             Ok(Stmt::Let(Box::new(var_def), init_expr, export, token_pos))
         }
         // const name = { expr:constant }
         AccessMode::ReadOnly => {
             let var_name = state.get_interned_string(name.clone());
             state.stack.push((var_name, AccessMode::ReadOnly));
-            let var_def = Ident::new(name, pos);
+            let var_def = IdentX::new(name, pos);
             Ok(Stmt::Const(Box::new(var_def), init_expr, export, token_pos))
         }
     }
diff --git a/src/scope.rs b/src/scope.rs
index 93b4ba7d..4e5cc08a 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -1,8 +1,8 @@
 //! Module that defines the [`Scope`] type representing a function call-stack scope.
 
 use crate::dynamic::{AccessMode, Variant};
-use crate::stdlib::{borrow::Cow, boxed::Box, iter, string::String, vec::Vec};
-use crate::{Dynamic, StaticVec};
+use crate::stdlib::{borrow::Cow, boxed::Box, iter, vec::Vec};
+use crate::{Dynamic, ImmutableString, StaticVec};
 
 /// Type containing information about the current scope.
 /// Useful for keeping state between [`Engine`][crate::Engine] evaluation runs.
@@ -50,7 +50,7 @@ pub struct Scope<'a> {
     /// Current value of the entry.
     values: Vec<Dynamic>,
     /// (Name, aliases) of the entry. The list of aliases is Boxed because it occurs rarely.
-    names: Vec<(Cow<'a, str>, Box<StaticVec<String>>)>,
+    names: Vec<(Cow<'a, str>, Box<StaticVec<ImmutableString>>)>,
 }
 
 impl Default for Scope<'_> {
@@ -364,10 +364,14 @@ impl<'a> Scope<'a> {
     /// Update the access type of an entry in the [`Scope`].
     #[cfg(not(feature = "no_module"))]
     #[inline(always)]
-    pub(crate) fn add_entry_alias(&mut self, index: usize, alias: String) -> &mut Self {
+    pub(crate) fn add_entry_alias(
+        &mut self,
+        index: usize,
+        alias: impl Into<ImmutableString> + PartialEq<ImmutableString>,
+    ) -> &mut Self {
         let entry = self.names.get_mut(index).expect("invalid index in Scope");
-        if !entry.1.contains(&alias) {
-            entry.1.push(alias);
+        if !entry.1.iter().any(|a| &alias == a) {
+            entry.1.push(alias.into());
         }
         self
     }
@@ -393,7 +397,9 @@ impl<'a> Scope<'a> {
     /// Get an iterator to entries in the [`Scope`].
     #[inline(always)]
     #[allow(dead_code)]
-    pub(crate) fn into_iter(self) -> impl Iterator<Item = (Cow<'a, str>, Dynamic, Vec<String>)> {
+    pub(crate) fn into_iter(
+        self,
+    ) -> impl Iterator<Item = (Cow<'a, str>, Dynamic, Vec<ImmutableString>)> {
         self.names
             .into_iter()
             .zip(self.values.into_iter())
diff --git a/tests/optimizer.rs b/tests/optimizer.rs
index db8477a5..fa817bf1 100644
--- a/tests/optimizer.rs
+++ b/tests/optimizer.rs
@@ -55,7 +55,7 @@ fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
 
     let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } else { 123 } }")?;
 
-    assert!(format!("{:?}", ast).starts_with(r#"AST([Block([Const(Ident { name: "DECISION", pos: 1:9 }, Some(Unit(0:0)), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)]"#));
+    assert!(format!("{:?}", ast).starts_with(r#"AST([Block([Const(IdentX { name: "DECISION", pos: 1:9 }, Some(Unit(0:0)), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)]"#));
 
     let ast = engine.compile("if 1 == 2 { 42 }")?;