Rollup merge of rust-lang#62249 - czipperz:use-mem-take-instead-of-replace-default, r=dtolnay,Centril

Use mem::take instead of mem::replace with default

Author: Centril

src/liballoc/collections/btree/map.rs

@@ -770,8 +770,8 @@ impl<K: Ord, V> BTreeMap<K, V> {
         }
 
         // First, we merge `self` and `other` into a sorted sequence in linear time.
-        let self_iter = mem::replace(self, BTreeMap::new()).into_iter();
-        let other_iter = mem::replace(other, BTreeMap::new()).into_iter();
+        let self_iter = mem::take(self).into_iter();
+        let other_iter = mem::take(other).into_iter();
         let iter = MergeIter {
             left: self_iter.peekable(),
             right: other_iter.peekable(),

src/liballoc/collections/linked_list.rs

@@ -708,7 +708,7 @@ impl<T> LinkedList<T> {
         let len = self.len();
         assert!(at <= len, "Cannot split off at a nonexistent index");
         if at == 0 {
-            return mem::replace(self, Self::new());
+            return mem::take(self);
         } else if at == len {
             return Self::new();
         }

src/liballoc/lib.rs

@@ -112,6 +112,7 @@
 #![feature(maybe_uninit_extra, maybe_uninit_slice, maybe_uninit_array)]
 #![feature(alloc_layout_extra)]
 #![feature(try_trait)]
+#![feature(mem_take)]
 
 // Allow testing this library
 

src/liballoc/str.rs

@@ -203,7 +203,7 @@ impl ToOwned for str {
     }
 
     fn clone_into(&self, target: &mut String) {
-        let mut b = mem::replace(target, String::new()).into_bytes();
+        let mut b = mem::take(target).into_bytes();
         self.as_bytes().clone_into(&mut b);
         *target = unsafe { String::from_utf8_unchecked(b) }
     }

src/libcore/lib.rs

@@ -126,6 +126,7 @@
 #![feature(adx_target_feature)]
 #![feature(maybe_uninit_slice, maybe_uninit_array)]
 #![feature(external_doc)]
+#![feature(mem_take)]
 
 #[prelude_import]
 #[allow(unused)]

src/libcore/option.rs

@@ -845,7 +845,7 @@ impl<T> Option<T> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn take(&mut self) -> Option<T> {
-        mem::replace(self, None)
+        mem::take(self)
     }
 
     /// Replaces the actual value in the option by the value given in parameter,

src/libproc_macro/bridge/buffer.rs

@@ -78,7 +78,7 @@ impl<T: Copy> Buffer<T> {
     }
 
     pub(super) fn take(&mut self) -> Self {
-        mem::replace(self, Self::default())
+        mem::take(self)
     }
 
     pub(super) fn extend_from_slice(&mut self, xs: &[T]) {

src/libproc_macro/lib.rs

@@ -25,6 +25,7 @@
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]
 #![feature(optin_builtin_traits)]
+#![feature(mem_take)]
 #![feature(non_exhaustive)]
 #![feature(specialization)]
 

src/librustc/hir/lowering.rs

@@ -1280,8 +1280,8 @@ impl<'a> LoweringContext<'a> {
         let was_in_loop_condition = self.is_in_loop_condition;
         self.is_in_loop_condition = false;
 
-        let catch_scopes = mem::replace(&mut self.catch_scopes, Vec::new());
-        let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
+        let catch_scopes = mem::take(&mut self.catch_scopes);
+        let loop_scopes = mem::take(&mut self.loop_scopes);
         let ret = f(self);
         self.catch_scopes = catch_scopes;
         self.loop_scopes = loop_scopes;

src/librustc/infer/nll_relate/mod.rs

@@ -364,7 +364,7 @@ where
         // been fully instantiated and hence the set of scopes we have
         // doesn't matter -- just to be sure, put an empty vector
         // in there.
-        let old_a_scopes = ::std::mem::replace(pair.vid_scopes(self), vec![]);
+        let old_a_scopes = ::std::mem::take(pair.vid_scopes(self));
 
         // Relate the generalized kind to the original one.
         let result = pair.relate_generalized_ty(self, generalized_ty);