diff --git a/src/api/custom_syntax.rs b/src/api/custom_syntax.rs
index ad7e5b40..080d4477 100644
--- a/src/api/custom_syntax.rs
+++ b/src/api/custom_syntax.rs
@@ -147,6 +147,7 @@ impl Expression<'_> {
 
 impl AsRef<Expr> for Expression<'_> {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &Expr {
         self.0
     }
@@ -156,6 +157,7 @@ impl Deref for Expression<'_> {
     type Target = Expr;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         self.0
     }
diff --git a/src/api/mod.rs b/src/api/mod.rs
index e9e03854..6ddf090b 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -75,6 +75,7 @@ impl Engine {
     /// Not available under `no_module`.
     #[cfg(not(feature = "no_module"))]
     #[inline(always)]
+    #[must_use]
     pub fn module_resolver(&self) -> &dyn crate::ModuleResolver {
         &*self.module_resolver
     }
diff --git a/src/api/register.rs b/src/api/register.rs
index 2b4e20ed..9095a31f 100644
--- a/src/api/register.rs
+++ b/src/api/register.rs
@@ -16,12 +16,14 @@ impl Engine {
     /// Get the global namespace module (which is the fist module in `global_modules`).
     #[inline(always)]
     #[allow(dead_code)]
+    #[must_use]
     pub(crate) fn global_namespace(&self) -> &Module {
         self.global_modules.first().unwrap()
     }
     /// Get a mutable reference to the global namespace module
     /// (which is the first module in `global_modules`).
     #[inline(always)]
+    #[must_use]
     pub(crate) fn global_namespace_mut(&mut self) -> &mut Module {
         let module = self.global_modules.first_mut().unwrap();
         Shared::get_mut(module).expect("not shared")
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index da0454fe..902a6856 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -919,6 +919,7 @@ impl<A: Into<Self>> AddAssign<A> for AST {
 
 impl AsRef<[Stmt]> for AST {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &[Stmt] {
         self.statements()
     }
@@ -927,6 +928,7 @@ impl AsRef<[Stmt]> for AST {
 #[cfg(not(feature = "no_function"))]
 impl AsRef<crate::Module> for AST {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &crate::Module {
         self.shared_lib().as_ref()
     }
@@ -935,6 +937,7 @@ impl AsRef<crate::Module> for AST {
 #[cfg(not(feature = "no_function"))]
 impl AsRef<crate::Shared<crate::Module>> for AST {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &crate::Shared<crate::Module> {
         self.shared_lib()
     }
diff --git a/src/ast/expr.rs b/src/ast/expr.rs
index 3b07ecfd..389ac137 100644
--- a/src/ast/expr.rs
+++ b/src/ast/expr.rs
@@ -257,6 +257,7 @@ impl Hash for FloatWrapper<crate::FLOAT> {
 #[cfg(not(feature = "no_float"))]
 impl<F: Float> AsRef<F> for FloatWrapper<F> {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &F {
         &self.0
     }
@@ -265,6 +266,7 @@ impl<F: Float> AsRef<F> for FloatWrapper<F> {
 #[cfg(not(feature = "no_float"))]
 impl<F: Float> AsMut<F> for FloatWrapper<F> {
     #[inline(always)]
+    #[must_use]
     fn as_mut(&mut self) -> &mut F {
         &mut self.0
     }
@@ -275,6 +277,7 @@ impl<F: Float> Deref for FloatWrapper<F> {
     type Target = F;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         &self.0
     }
@@ -283,6 +286,7 @@ impl<F: Float> Deref for FloatWrapper<F> {
 #[cfg(not(feature = "no_float"))]
 impl<F: Float> DerefMut for FloatWrapper<F> {
     #[inline(always)]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }
diff --git a/src/ast/ident.rs b/src/ast/ident.rs
index 13ab4ef9..8a6d98aa 100644
--- a/src/ast/ident.rs
+++ b/src/ast/ident.rs
@@ -28,6 +28,7 @@ impl fmt::Debug for Ident {
 
 impl AsRef<str> for Ident {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &str {
         self.name.as_ref()
     }
@@ -37,6 +38,7 @@ impl Deref for Ident {
     type Target = ImmutableString;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         &self.name
     }
@@ -44,6 +46,7 @@ impl Deref for Ident {
 
 impl DerefMut for Ident {
     #[inline(always)]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.name
     }
diff --git a/src/ast/namespace.rs b/src/ast/namespace.rs
index 800dba52..9dba5b18 100644
--- a/src/ast/namespace.rs
+++ b/src/ast/namespace.rs
@@ -70,6 +70,7 @@ impl Deref for Namespace {
     type Target = StaticVec<Ident>;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         &self.path
     }
@@ -77,6 +78,7 @@ impl Deref for Namespace {
 
 impl DerefMut for Namespace {
     #[inline(always)]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.path
     }
diff --git a/src/ast/stmt.rs b/src/ast/stmt.rs
index 68b63ecd..3b830100 100644
--- a/src/ast/stmt.rs
+++ b/src/ast/stmt.rs
@@ -424,6 +424,7 @@ impl Deref for StmtBlock {
     type Target = StmtBlockContainer;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         &self.block
     }
@@ -431,6 +432,7 @@ impl Deref for StmtBlock {
 
 impl DerefMut for StmtBlock {
     #[inline(always)]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.block
     }
@@ -438,6 +440,7 @@ impl DerefMut for StmtBlock {
 
 impl AsRef<[Stmt]> for StmtBlock {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &[Stmt] {
         &self.block
     }
@@ -445,6 +448,7 @@ impl AsRef<[Stmt]> for StmtBlock {
 
 impl AsMut<[Stmt]> for StmtBlock {
     #[inline(always)]
+    #[must_use]
     fn as_mut(&mut self) -> &mut [Stmt] {
         &mut self.block
     }
diff --git a/src/engine.rs b/src/engine.rs
index 3520108f..72f95c6b 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -240,12 +240,12 @@ impl Engine {
                 source.map_or_else(
                     || {
                         if pos.is_none() {
-                            println!("{}", s);
+                            println!("{s}");
                         } else {
-                            println!("{:?} | {}", pos, s);
+                            println!("{pos:?} | {s}");
                         }
                     },
-                    |source| println!("{} @ {:?} | {}", source, pos, s),
+                    |source| println!("{source} @ {pos:?} | {s}"),
                 )
             });
         }
diff --git a/src/eval/target.rs b/src/eval/target.rs
index 9c0804ab..3b47533d 100644
--- a/src/eval/target.rs
+++ b/src/eval/target.rs
@@ -399,6 +399,7 @@ impl Deref for Target<'_> {
     type Target = Dynamic;
 
     #[inline]
+    #[must_use]
     fn deref(&self) -> &Dynamic {
         match self {
             Self::RefMut(r) => r,
@@ -416,6 +417,7 @@ impl Deref for Target<'_> {
 
 impl AsRef<Dynamic> for Target<'_> {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &Dynamic {
         self
     }
@@ -423,6 +425,7 @@ impl AsRef<Dynamic> for Target<'_> {
 
 impl DerefMut for Target<'_> {
     #[inline]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Dynamic {
         match self {
             Self::RefMut(r) => r,
@@ -440,6 +443,7 @@ impl DerefMut for Target<'_> {
 
 impl AsMut<Dynamic> for Target<'_> {
     #[inline(always)]
+    #[must_use]
     fn as_mut(&mut self) -> &mut Dynamic {
         self
     }
diff --git a/src/module/resolvers/file.rs b/src/module/resolvers/file.rs
index ee71ce13..729e772f 100644
--- a/src/module/resolvers/file.rs
+++ b/src/module/resolvers/file.rs
@@ -194,8 +194,8 @@ impl FileModuleResolver {
     /// Get a reference to the file module resolver's [scope][Scope].
     ///
     /// The [scope][Scope] is used for compiling module scripts.
-    #[must_use]
     #[inline(always)]
+    #[must_use]
     pub const fn scope(&self) -> &Scope {
         &self.scope
     }
@@ -211,8 +211,8 @@ impl FileModuleResolver {
     /// Get a mutable reference to the file module resolver's [scope][Scope].
     ///
     /// The [scope][Scope] is used for compiling module scripts.
-    #[must_use]
     #[inline(always)]
+    #[must_use]
     pub fn scope_mut(&mut self) -> &mut Scope<'static> {
         &mut self.scope
     }
diff --git a/src/types/dynamic.rs b/src/types/dynamic.rs
index 6823dd74..b310b302 100644
--- a/src/types/dynamic.rs
+++ b/src/types/dynamic.rs
@@ -252,6 +252,7 @@ impl<'d, T: Any + Clone> Deref for DynamicWriteLock<'d, T> {
     type Target = T;
 
     #[inline]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         match self.0 {
             DynamicWriteLockInner::Reference(ref reference) => *reference,
@@ -263,6 +264,7 @@ impl<'d, T: Any + Clone> Deref for DynamicWriteLock<'d, T> {
 
 impl<'d, T: Any + Clone> DerefMut for DynamicWriteLock<'d, T> {
     #[inline]
+    #[must_use]
     fn deref_mut(&mut self) -> &mut Self::Target {
         match self.0 {
             DynamicWriteLockInner::Reference(ref mut reference) => *reference,
diff --git a/src/types/error.rs b/src/types/error.rs
index d426d5ed..822b1a39 100644
--- a/src/types/error.rs
+++ b/src/types/error.rs
@@ -23,6 +23,7 @@ use std::prelude::v1::*;
 /// Turn on the `sync` feature to make it [`Send`] `+` [`Sync`].
 #[derive(Debug)]
 #[non_exhaustive]
+#[must_use]
 pub enum EvalAltResult {
     /// System error. Wrapped values are the error message and the internal error.
     #[cfg(not(feature = "sync"))]
@@ -494,6 +495,7 @@ impl EvalAltResult {
     /// The [position][Position] of this error is set to [`NONE`][Position::NONE] afterwards.
     #[cold]
     #[inline(never)]
+    #[must_use]
     pub fn take_position(&mut self) -> Position {
         let pos = self.position();
         self.set_position(Position::NONE);
diff --git a/src/types/immutable_string.rs b/src/types/immutable_string.rs
index 6487efeb..507c33d6 100644
--- a/src/types/immutable_string.rs
+++ b/src/types/immutable_string.rs
@@ -53,6 +53,7 @@ impl Deref for ImmutableString {
     type Target = SmartString;
 
     #[inline(always)]
+    #[must_use]
     fn deref(&self) -> &Self::Target {
         &self.0
     }
@@ -60,6 +61,7 @@ impl Deref for ImmutableString {
 
 impl AsRef<SmartString> for ImmutableString {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &SmartString {
         &self.0
     }
@@ -67,6 +69,7 @@ impl AsRef<SmartString> for ImmutableString {
 
 impl AsRef<str> for ImmutableString {
     #[inline(always)]
+    #[must_use]
     fn as_ref(&self) -> &str {
         &self.0
     }
@@ -74,6 +77,7 @@ impl AsRef<str> for ImmutableString {
 
 impl Borrow<SmartString> for ImmutableString {
     #[inline(always)]
+    #[must_use]
     fn borrow(&self) -> &SmartString {
         &self.0
     }
@@ -81,6 +85,7 @@ impl Borrow<SmartString> for ImmutableString {
 
 impl Borrow<str> for ImmutableString {
     #[inline(always)]
+    #[must_use]
     fn borrow(&self) -> &str {
         self.as_str()
     }
@@ -623,7 +628,7 @@ impl ImmutableString {
     #[inline]
     #[must_use]
     pub fn into_owned(mut self) -> String {
-        self.make_mut(); // Make sure it is unique reference
+        let _ = self.make_mut(); // Make sure it is unique reference
         shared_take(self.0).into() // Should succeed
     }
     /// Make sure that the [`ImmutableString`] is unique (i.e. no other outstanding references).
@@ -631,6 +636,7 @@ impl ImmutableString {
     ///
     /// If there are other references to the same string, a cloned copy is used.
     #[inline(always)]
+    #[must_use]
     pub(crate) fn make_mut(&mut self) -> &mut SmartString {
         shared_make_mut(&mut self.0)
     }
diff --git a/src/types/parse_error.rs b/src/types/parse_error.rs
index 5cbdcb5d..e9b55ce3 100644
--- a/src/types/parse_error.rs
+++ b/src/types/parse_error.rs
@@ -13,6 +13,7 @@ use std::prelude::v1::*;
 /// Error encountered when tokenizing the script text.
 #[derive(Debug, Eq, PartialEq, Clone, Hash)]
 #[non_exhaustive]
+#[must_use]
 pub enum LexError {
     /// An unexpected symbol is encountered when tokenizing the script text.
     UnexpectedInput(String),
@@ -58,8 +59,8 @@ impl fmt::Display for LexError {
 
 impl LexError {
     /// Convert a [`LexError`] into a [`ParseError`].
-    #[inline(always)]
-    #[must_use]
+    #[cold]
+    #[inline(never)]
     pub fn into_err(self, pos: Position) -> ParseError {
         ParseError(Box::new(self.into()), pos)
     }
@@ -72,6 +73,7 @@ impl LexError {
 /// massive code changes to remove/add back enum variants in match statements.
 #[derive(Debug, Eq, PartialEq, Clone, Hash)]
 #[non_exhaustive]
+#[must_use]
 pub enum ParseErrorType {
     /// The script ends prematurely.
     UnexpectedEOF,
@@ -171,7 +173,8 @@ pub enum ParseErrorType {
 
 impl ParseErrorType {
     /// Make a [`ParseError`] using the current type and position.
-    #[inline(always)]
+    #[cold]
+    #[inline(never)]
     #[must_use]
     pub(crate) fn into_err(self, pos: Position) -> ParseError {
         ParseError(self.into(), pos)
@@ -277,6 +280,7 @@ impl From<LexError> for ParseErrorType {
 
 /// Error when parsing a script.
 #[derive(Debug, Eq, PartialEq, Clone, Hash)]
+#[must_use]
 pub struct ParseError(
     /// Parse error type.
     pub Box<ParseErrorType>,
diff --git a/tests/operations.rs b/tests/operations.rs
index d6b7b69f..c4eb37ab 100644
--- a/tests/operations.rs
+++ b/tests/operations.rs
@@ -10,7 +10,7 @@ fn test_max_operations() -> Result<(), Box<EvalAltResult>> {
 
     engine.on_progress(|count| {
         if count % 100 == 0 {
-            println!("{}", count);
+            println!("{count}");
         }
         None
     });
@@ -68,7 +68,7 @@ fn test_max_operations_functions() -> Result<(), Box<EvalAltResult>> {
 
     engine.on_progress(|count| {
         if count % 100 == 0 {
-            println!("{}", count);
+            println!("{count}");
         }
         None
     });
@@ -124,7 +124,7 @@ fn test_max_operations_eval() -> Result<(), Box<EvalAltResult>> {
 
     engine.on_progress(|count| {
         if count % 100 == 0 {
-            println!("{}", count);
+            println!("{count}");
         }
         None
     });
diff --git a/tests/plugins.rs b/tests/plugins.rs
index d5072eb9..5fe58fdc 100644
--- a/tests/plugins.rs
+++ b/tests/plugins.rs
@@ -42,7 +42,7 @@ mod test {
         #[rhai_fn(name = "no_effect", set = "no_effect", pure)]
         pub fn no_effect(array: &mut Array, value: INT) {
             // array is not modified
-            println!("Array = {:?}, Value = {}", array, value);
+            println!("Array = {array:?}, Value = {value}");
         }
     }
 }
diff --git a/tests/print.rs b/tests/print.rs
index 820cce58..982b2ff2 100644
--- a/tests/print.rs
+++ b/tests/print.rs
@@ -66,7 +66,7 @@ fn test_print_debug() -> Result<(), Box<EvalAltResult>> {
     );
 
     for entry in logbook.read().unwrap().iter() {
-        println!("{}", entry);
+        println!("{entry}");
     }
 
     Ok(())
diff --git a/tests/serde.rs b/tests/serde.rs
index 5df11139..45c16b72 100644
--- a/tests/serde.rs
+++ b/tests/serde.rs
@@ -820,6 +820,6 @@ fn test_serde_blob() -> Result<(), Box<EvalAltResult>> {
 #[cfg(not(feature = "no_object"))]
 fn test_serde_json_borrowed_string() {
     let value = json!({ "a": "b" });
-    println!("value: {:?}", value);
+    println!("value: {value:?}");
     let _: Dynamic = serde_json::from_value(value).unwrap();
 }
diff --git a/tests/var_scope.rs b/tests/var_scope.rs
index 73701746..e249b6de 100644
--- a/tests/var_scope.rs
+++ b/tests/var_scope.rs
@@ -140,7 +140,7 @@ fn test_scope_eval() -> Result<(), Box<EvalAltResult>> {
     // Second invocation using the same state
     let result = engine.eval_with_scope::<INT>(&mut scope, "x")?;
 
-    println!("result: {}", result); // should print 966
+    println!("result: {result}"); // should print 966
 
     // Variable y is changed in the script
     assert_eq!(