Reduce API changes.

src/engine.rs

@@ -308,9 +308,10 @@ impl Engine {
         engine
     }
 
-    /// Get an interned string.
-    #[must_use]
+    /// Get an interned [string][ImmutableString].
+    #[cfg(not(feature = "internals"))]
     #[inline(always)]
+    #[must_use]
     pub(crate) fn get_interned_string(
         &self,
         string: impl AsRef<str> + Into<ImmutableString>,
@@ -318,6 +319,28 @@ impl Engine {
         locked_write(&self.interned_strings).get(string).into()
     }
 
+    /// _(internals)_ Get an interned [string][ImmutableString].
+    /// Exported under the `internals` feature only.
+    ///
+    /// [`Engine`] keeps a cache of [`ImmutableString`] instances and tries to avoid new allocations
+    /// when an existing instance is found.
+    #[cfg(feature = "internals")]
+    #[inline(always)]
+    #[must_use]
+    pub fn get_interned_string(
+        &self,
+        string: impl AsRef<str> + Into<ImmutableString>,
+    ) -> ImmutableString {
+        locked_write(&self.interned_strings).get(string).into()
+    }
+
+    /// Get an empty [`ImmutableString`] which refers to a shared instance.
+    #[inline(always)]
+    #[must_use]
+    pub fn const_empty_string(&self) -> ImmutableString {
+        self.get_interned_string("")
+    }
+
     /// Check a result to ensure that it is valid.
     #[inline]
     pub(crate) fn check_return_value(&self, result: RhaiResult, _pos: Position) -> RhaiResult {

src/eval/eval_context.rs

@@ -6,6 +6,7 @@ use crate::{Dynamic, Engine, Module, Scope};
 use std::prelude::v1::*;
 
 /// Context of a script evaluation process.
+#[derive(Debug)]
 #[allow(dead_code)]
 pub struct EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 'pc, 't, 'pt> {
     /// The current [`Engine`].

src/tokenizer.rs

@@ -20,7 +20,7 @@ use std::{
 };
 
 /// _(internals)_ A type containing commands to control the tokenizer.
-#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+#[derive(Debug, Clone, Eq, PartialEq, Default, Hash)]
 pub struct TokenizerControlBlock {
     /// Is the current tokenizer position within an interpolated text string?
     /// This flag allows switching the tokenizer back to _text_ parsing after an interpolation stream.
@@ -1117,7 +1117,7 @@ impl From<Token> for String {
 
 /// _(internals)_ State of the tokenizer.
 /// Exported under the `internals` feature only.
-#[derive(Debug, Clone, Eq, PartialEq)]
+#[derive(Debug, Clone, Eq, PartialEq, Default)]
 pub struct TokenizeState {
     /// Maximum length of a string.
     pub max_string_size: Option<NonZeroUsize>,