More mem::take in library

A bunch of places were using `replace(…, &mut [])`, but that can just be `take`.

library/alloc/src/vec/drain.rs

@@ -197,7 +197,7 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
             }
         }
 
-        let iter = mem::replace(&mut self.iter, (&mut []).iter());
+        let iter = mem::take(&mut self.iter);
         let drop_len = iter.len();
 
         let mut vec = self.vec;

library/core/src/slice/iter.rs

@@ -685,7 +685,7 @@ where
             None
         } else {
             self.finished = true;
-            Some(mem::replace(&mut self.v, &mut []))
+            Some(mem::take(&mut self.v))
         }
     }
 }
@@ -749,7 +749,7 @@ where
         match idx_opt {
             None => self.finish(),
             Some(idx) => {
-                let tmp = mem::replace(&mut self.v, &mut []);
+                let tmp = mem::take(&mut self.v);
                 let (head, tail) = tmp.split_at_mut(idx);
                 self.v = head;
                 Some(&mut tail[1..])
@@ -830,7 +830,7 @@ where
         if idx == self.v.len() {
             self.finished = true;
         }
-        let tmp = mem::replace(&mut self.v, &mut []);
+        let tmp = mem::take(&mut self.v);
         let (head, tail) = tmp.split_at_mut(idx);
         self.v = tail;
         Some(head)
@@ -876,7 +876,7 @@ where
         if idx == 0 {
             self.finished = true;
         }
-        let tmp = mem::replace(&mut self.v, &mut []);
+        let tmp = mem::take(&mut self.v);
         let (head, tail) = tmp.split_at_mut(idx);
         self.v = head;
         Some(tail)

library/std/src/io/impls.rs

@@ -336,7 +336,7 @@ impl Write for &mut [u8] {
     #[inline]
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         let amt = cmp::min(data.len(), self.len());
-        let (a, b) = mem::replace(self, &mut []).split_at_mut(amt);
+        let (a, b) = mem::take(self).split_at_mut(amt);
         a.copy_from_slice(&data[..amt]);
         *self = b;
         Ok(amt)

library/std/src/io/mod.rs

@@ -253,7 +253,7 @@ mod tests;
 
 use crate::cmp;
 use crate::fmt;
-use crate::mem::replace;
+use crate::mem::take;
 use crate::ops::{Deref, DerefMut};
 use crate::slice;
 use crate::str;
@@ -1186,7 +1186,7 @@ impl<'a> IoSliceMut<'a> {
             }
         }
 
-        *bufs = &mut replace(bufs, &mut [])[remove..];
+        *bufs = &mut take(bufs)[remove..];
         if bufs.is_empty() {
             assert!(n == accumulated_len, "advancing io slices beyond their length");
         } else {
@@ -1329,7 +1329,7 @@ impl<'a> IoSlice<'a> {
             }
         }
 
-        *bufs = &mut replace(bufs, &mut [])[remove..];
+        *bufs = &mut take(bufs)[remove..];
         if bufs.is_empty() {
             assert!(n == accumulated_len, "advancing io slices beyond their length");
         } else {

library/std/src/sys/unsupported/io.rs

@@ -30,7 +30,7 @@ impl<'a> IoSliceMut<'a> {
 
     #[inline]
     pub fn advance(&mut self, n: usize) {
-        let slice = mem::replace(&mut self.0, &mut []);
+        let slice = mem::take(&mut self.0);
         let (_, remaining) = slice.split_at_mut(n);
         self.0 = remaining;
     }