diff --git a/src/minify/attr.rs b/src/minify/attr.rs
index a0a25a9..bb9e4cd 100644
--- a/src/minify/attr.rs
+++ b/src/minify/attr.rs
@@ -150,7 +150,7 @@ impl AttrValMinified {
         self.prefix.len() + (self.data.len() - self.start) + self.suffix.len()
     }
 
-    pub fn out(&self, out: &mut Vec<u8>) -> () {
+    pub fn out(&self, out: &mut Vec<u8>) {
         out.extend_from_slice(self.prefix);
         out.extend_from_slice(&self.data[self.start..]);
         out.extend_from_slice(self.suffix);
diff --git a/src/minify/bang.rs b/src/minify/bang.rs
index 2f3c882..ba55e10 100644
--- a/src/minify/bang.rs
+++ b/src/minify/bang.rs
@@ -1,9 +1,9 @@
 use crate::cfg::Cfg;
 
-pub fn minify_bang(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) -> () {
+pub fn minify_bang(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) {
     if !cfg.remove_bangs {
         out.extend_from_slice(b"<!");
-        out.extend_from_slice(&code);
+        out.extend_from_slice(code);
         if ended {
             out.extend_from_slice(b">");
         };
diff --git a/src/minify/comment.rs b/src/minify/comment.rs
index edb1ed5..0ab2733 100644
--- a/src/minify/comment.rs
+++ b/src/minify/comment.rs
@@ -1,9 +1,9 @@
 use crate::cfg::Cfg;
 
-pub fn minify_comment(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) -> () {
+pub fn minify_comment(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) {
     if !cfg.remove_comments {
         out.extend_from_slice(b"<!--");
-        out.extend_from_slice(&code);
+        out.extend_from_slice(code);
         if ended {
             out.extend_from_slice(b"-->");
         };
diff --git a/src/minify/content.rs b/src/minify/content.rs
index 80afde4..01c7264 100644
--- a/src/minify/content.rs
+++ b/src/minify/content.rs
@@ -48,7 +48,7 @@ pub fn minify_content(
     // Use empty slice if none.
     parent: &[u8],
     mut nodes: Vec<NodeData>,
-) -> () {
+) {
     let &WhitespaceMinification {
         collapse,
         destroy_whole,
diff --git a/src/minify/css.rs b/src/minify/css.rs
index 43523de..9618d8a 100644
--- a/src/minify/css.rs
+++ b/src/minify/css.rs
@@ -1,6 +1,6 @@
 use crate::cfg::Cfg;
 
-pub fn minify_css(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8]) -> () {
+pub fn minify_css(_cfg: &Cfg, out: &mut Vec<u8>, code: &[u8]) {
     // TODO
     out.extend_from_slice(code);
 }
diff --git a/src/minify/element.rs b/src/minify/element.rs
index b891ffd..cb8a515 100644
--- a/src/minify/element.rs
+++ b/src/minify/element.rs
@@ -22,7 +22,7 @@ pub fn minify_element(
     attributes: HashMap<Vec<u8>, Vec<u8>>,
     closing_tag: ElementClosingTag,
     children: Vec<NodeData>,
-) -> () {
+) {
     let can_omit_closing_tag = cfg.omit_closing_tags
         && (can_omit_as_before(tag_name, next_sibling_as_element_tag_name)
             || (is_last_child_text_or_element_node && can_omit_as_last_node(parent, tag_name)));
diff --git a/src/minify/instruction.rs b/src/minify/instruction.rs
index 36ffcf6..ff29a43 100644
--- a/src/minify/instruction.rs
+++ b/src/minify/instruction.rs
@@ -1,9 +1,9 @@
 use crate::cfg::Cfg;
 
-pub fn minify_instruction(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) -> () {
+pub fn minify_instruction(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8], ended: bool) {
     if !cfg.remove_processing_instructions {
         out.extend_from_slice(b"<?");
-        out.extend_from_slice(&code);
+        out.extend_from_slice(code);
         if ended {
             out.extend_from_slice(b"?>");
         };
diff --git a/src/minify/js.rs b/src/minify/js.rs
index 9b20c4f..8a85b0a 100644
--- a/src/minify/js.rs
+++ b/src/minify/js.rs
@@ -1,6 +1,6 @@
 use crate::cfg::Cfg;
 
-pub fn minify_js(cfg: &Cfg, out: &mut Vec<u8>, code: &[u8]) -> () {
+pub fn minify_js(_cfg: &Cfg, out: &mut Vec<u8>, code: &[u8]) {
     // TODO
     out.extend_from_slice(code);
 }
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 6a0c91b..cd6474d 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -32,7 +32,7 @@ impl<'c> Code<'c> {
         Checkpoint(self.next)
     }
 
-    pub fn restore_checkpoint(&mut self, cp: Checkpoint) -> () {
+    pub fn restore_checkpoint(&mut self, cp: Checkpoint) {
         self.next = cp.0;
     }
 
@@ -51,7 +51,7 @@ impl<'c> Code<'c> {
     }
 
     pub fn shift_if_next_in_lookup(&mut self, lookup: &'static Lookup) -> Option<u8> {
-        let c = self.code.get(self.next).filter(|&&n| lookup[n]).map(|&c| c);
+        let c = self.code.get(self.next).filter(|&&n| lookup[n]).copied();
         if c.is_some() {
             self.next += 1;
         };
@@ -62,15 +62,14 @@ impl<'c> Code<'c> {
         let c = self
             .code
             .get(self.next)
-            .filter(|&&n| !lookup[n])
-            .map(|&c| c);
+            .filter(|&&n| !lookup[n]).copied();
         if c.is_some() {
             self.next += 1;
         };
         c
     }
 
-    pub fn shift(&mut self, n: usize) -> () {
+    pub fn shift(&mut self, n: usize) {
         self.next += n;
     }
 
diff --git a/src/spec/entity/decode.rs b/src/spec/entity/decode.rs
index 2c212e3..7349945 100644
--- a/src/spec/entity/decode.rs
+++ b/src/spec/entity/decode.rs
@@ -68,7 +68,7 @@ fn parse_numeric_entity(
     // Browsers decode to a replacement character (U+FFFD) if malformed.
     let char = Some(value)
         .filter(|_| digits <= max_digits)
-        .and_then(|v| from_u32(v))
+        .and_then(from_u32)
         .unwrap_or('\u{FFFD}');
     ParsedEntity {
         read_len: read_next,
diff --git a/src/spec/tag/mod.rs b/src/spec/tag/mod.rs
index 0df2160..13d1485 100644
--- a/src/spec/tag/mod.rs
+++ b/src/spec/tag/mod.rs
@@ -3,4 +3,4 @@ pub mod omission;
 pub mod void;
 pub mod whitespace;
 
-pub static EMPTY_SLICE: &'static [u8] = &[];
+pub static EMPTY_SLICE: &[u8] = &[];
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
index 70bf1e7..7654784 100644
--- a/src/tests/mod.rs
+++ b/src/tests/mod.rs
@@ -1,4 +1,4 @@
-fn _eval(src: &'static [u8], expected: &'static [u8], cfg: &super::Cfg) -> () {
+fn _eval(src: &'static [u8], expected: &'static [u8], cfg: &super::Cfg) {
     let mut code = src.to_vec();
     let min = super::minify(&mut code, cfg);
     assert_eq!(
@@ -7,7 +7,7 @@ fn _eval(src: &'static [u8], expected: &'static [u8], cfg: &super::Cfg) -> () {
     );
 }
 
-fn eval(src: &'static [u8], expected: &'static [u8]) -> () {
+fn eval(src: &'static [u8], expected: &'static [u8]) {
     _eval(
         src,
         expected,
diff --git a/src/whitespace.rs b/src/whitespace.rs
index 3353d3e..81ed0ae 100644
--- a/src/whitespace.rs
+++ b/src/whitespace.rs
@@ -1,6 +1,6 @@
 use crate::gen::codepoints::WHITESPACE;
 
-pub fn left_trim(val: &mut Vec<u8>) -> () {
+pub fn left_trim(val: &mut Vec<u8>) {
     let mut len = 0;
     while val.get(len).filter(|&&c| WHITESPACE[c]).is_some() {
         len += 1;
@@ -8,7 +8,7 @@ pub fn left_trim(val: &mut Vec<u8>) -> () {
     val.drain(0..len);
 }
 
-pub fn right_trim(val: &mut Vec<u8>) -> () {
+pub fn right_trim(val: &mut Vec<u8>) {
     let mut retain = val.len();
     while retain > 0 && val.get(retain - 1).filter(|&&c| WHITESPACE[c]).is_some() {
         retain -= 1;
@@ -16,7 +16,7 @@ pub fn right_trim(val: &mut Vec<u8>) -> () {
     val.truncate(retain);
 }
 
-pub fn collapse_whitespace(val: &mut Vec<u8>) -> () {
+pub fn collapse_whitespace(val: &mut Vec<u8>) {
     let mut write = 0;
     let mut in_whitespace = false;
     for i in 0..val.len() {