diff -r ad16acf47726 -r 016122e0384b src/maputil.rs
--- a/src/maputil.rs	Mon Aug 03 19:26:21 2026 -0500
+++ b/src/maputil.rs	Tue Aug 04 14:53:58 2026 -0500
@@ -80,7 +80,7 @@
         >(
             $var0 : $ctype0,
             $($var : $ctype,)*
-            f : impl Fn($etype0, $($etype),*) -> Res
+            mut f : impl FnMut($etype0, $($etype),*) -> Res
         ) -> [Res; N] {
             let zipit = izip!($var0.fl_iter(), $($var.fl_iter()),*);
             let map = zipit.map(|tuple_or_singleton!($var0, $($var),*)| f($var0, $($var),*));
@@ -99,7 +99,7 @@
         >(
             $var0 : $ctype0,
             $($var : $ctype,)*
-            f : impl Fn(usize, $etype0, $($etype),*) -> Res
+            mut f : impl FnMut(usize, $etype0, $($etype),*) -> Res
         ) -> [Res; N] {
             let zipit = (0..N).zip(izip!($var0.fl_iter(), $($var.fl_iter()),*));
             let map = zipit.map(|(i, tuple_or_singleton!($var0, $($var),*))| f(i, $var0, $($var),*));
@@ -263,11 +263,7 @@
         F: Fn(usize, &'a A) -> B;
     #[inline]
     fn indexmap<B, F: Fn(usize, &'a A) -> B>(self, f: F) -> Self::Output<B, F> {
-        IndexMap {
-            iter: self,
-            j: 0,
-            f,
-        }
+        IndexMap { iter: self, j: 0, f }
     }
 }
 
@@ -289,11 +285,7 @@
         F: Fn(usize, A) -> B;
     #[inline]
     fn indexmap<B, F: Fn(usize, A) -> B>(self, f: F) -> Self::Output<B, F> {
-        IndexMap {
-            iter: self,
-            j: 0,
-            f,
-        }
+        IndexMap { iter: self, j: 0, f }
     }
 }
 
@@ -382,10 +374,7 @@
     }
 
     let mut array = [const { MaybeUninit::uninit() }; N];
-    let mut guard = Guard {
-        array_mut: &mut array,
-        initialized: 0,
-    };
+    let mut guard = Guard { array_mut: &mut array, initialized: 0 };
 
     while let Some(item) = iter.next() {
         // SAFETY: `guard.initialized` starts at 0, is increased by one in the