diff --git a/compiler/erg_common/astr.rs b/compiler/erg_common/astr.rs
index fa082381..1c45b313 100644
--- a/compiler/erg_common/astr.rs
+++ b/compiler/erg_common/astr.rs
@@ -36,7 +36,7 @@ impl Add<&str> for AtomicStr {
 impl Hash for AtomicStr {
     fn hash<H: Hasher>(&self, state: &mut H) {
         match self {
-            AtomicStr::Arc(s) => (&s[..]).hash(state),
+            AtomicStr::Arc(s) => s[..].hash(state),
             AtomicStr::Static(s) => (*s).hash(state),
         }
     }
diff --git a/compiler/erg_common/levenshtein.rs b/compiler/erg_common/levenshtein.rs
index 1e0910cf..8d8a674e 100644
--- a/compiler/erg_common/levenshtein.rs
+++ b/compiler/erg_common/levenshtein.rs
@@ -7,18 +7,16 @@ pub fn levenshtein(lhs: &str, rhs: &str) -> usize {
     let r_len = rhs.len();
     // l_len+1 × r_len+1 array
     let mut table = vec![vec![0; r_len + 1]; l_len + 1];
-    let _ = table
+    table
         .iter_mut()
         .take(l_len + 1)
         .enumerate()
-        .map(|(i, row)| row[0] = i)
-        .collect::<()>();
-    let _ = table[0]
+        .for_each(|(i, row)| row[0] = i);
+    table[0]
         .iter_mut()
         .take(r_len + 1)
         .enumerate()
-        .map(|(i, elem)| *elem = i)
-        .collect::<()>();
+        .for_each(|(i, elem)| *elem = i);
     for i1 in 0..l_len {
         #[allow(clippy::needless_range_loop)]
         for i2 in 0..r_len {
diff --git a/compiler/erg_common/str.rs b/compiler/erg_common/str.rs
index 2ad73d54..cde076e5 100644
--- a/compiler/erg_common/str.rs
+++ b/compiler/erg_common/str.rs
@@ -32,7 +32,7 @@ impl Add<&str> for Str {
 impl Hash for Str {
     fn hash<H: Hasher>(&self, state: &mut H) {
         match self {
-            Str::Rc(s) => (&s[..]).hash(state),
+            Str::Rc(s) => s[..].hash(state),
             Str::Static(s) => (*s).hash(state),
         }
     }