Rename copy_from -> copy_from_slice

Author: ubsan

text/0000-slice-copy.md

@@ -22,13 +22,14 @@ Add one method to Primitive Type `slice`.
 
 ```rust
 impl<T> [T] where T: Copy {
-    pub fn copy_from(&mut self, src: &[T]);
+    pub fn copy_from_slice(&mut self, src: &[T]);
 }
 ```
 
-`copy_from` asserts that `src.len() == self.len()`, then `memcpy`s the members into 
-`self` from `src`. Calling `copy_from` is semantically equivalent to a `memcpy`.
-`self` shall have exactly the same members as `src` after a call to `copy_from`.
+`copy_from_slice` asserts that `src.len() == self.len()`, then `memcpy`s the
+members into `self` from `src`. Calling `copy_from_slice` is semantically
+equivalent to a `memcpy`.  `self` shall have exactly the same members as `src`
+after a call to `copy_from_slice`.
 
 # Drawbacks
 [drawbacks]: #drawbacks
@@ -38,19 +39,20 @@ One new method on `slice`.
 # Alternatives
 [alternatives]: #alternatives
 
-`copy_from` could be known as `copy_from_slice`, which would follow
-`clone_from_slice`.
-
-`copy_from` could be called `copy_to`, and have the order of the arguments
+`copy_from_slice` could be called `copy_to`, and have the order of the arguments
 switched around. This would follow `ptr::copy_nonoverlapping` ordering, and not
-`dst = src` or `.clone_from()` ordering.
+`dst = src` or `.clone_from_slice()` ordering.
+
+`copy_from_slice` could panic only if `dst.len() < src.len()`. This would be the
+same as what came before, but we would also lose the guarantee that an
+uninitialized slice would be fully initialized.
 
-`copy_from` could panic only if `dst.len() < src.len()`. This would be the same
-as what came before, but we would also lose the guarantee that an uninitialized
-slice would be fully initialized.
+`copy_from_slice` could be a free function, as it was in the original draft of
+this document. However, there was overwhelming support for it as a method.
 
-`copy_from` could be a free function, as it was in the original draft of this
-document. However, there was overwhelming support for it as a method.
+`copy_from_slice` could be not merged, and `clone_from_slice` could be
+specialized to `memcpy` in cases of `T: Copy`. I think it's good to have a
+specific function to do this, however, which asserts that `T: Copy`.
 
 # Unresolved questions
 [unresolved]: #unresolved-questions