Write for Cursor with a custom Allocator

library/std/src/io/cursor.rs

@@ -3,6 +3,7 @@ mod tests;
 
 use crate::io::prelude::*;
 
+use crate::alloc::Allocator;
 use crate::cmp;
 use crate::io::{self, Error, ErrorKind, IoSlice, IoSliceMut, ReadBuf, SeekFrom};
 
@@ -398,7 +399,10 @@ fn slice_write_vectored(
 }
 
 // Resizing write implementation
-fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usize> {
+fn vec_write<A>(pos_mut: &mut u64, vec: &mut Vec<u8, A>, buf: &[u8]) -> io::Result<usize>
+where
+    A: Allocator,
+{
     let pos: usize = (*pos_mut).try_into().map_err(|_| {
         Error::new_const(
             ErrorKind::InvalidInput,
@@ -426,11 +430,14 @@ fn vec_write(pos_mut: &mut u64, vec: &mut Vec<u8>, buf: &[u8]) -> io::Result<usi
     Ok(buf.len())
 }
 
-fn vec_write_vectored(
+fn vec_write_vectored<A>(
     pos_mut: &mut u64,
-    vec: &mut Vec<u8>,
+    vec: &mut Vec<u8, A>,
     bufs: &[IoSlice<'_>],
-) -> io::Result<usize> {
+) -> io::Result<usize>
+where
+    A: Allocator,
+{
     let mut nwritten = 0;
     for buf in bufs {
         nwritten += vec_write(pos_mut, vec, buf)?;
@@ -462,7 +469,10 @@ impl Write for Cursor<&mut [u8]> {
 }
 
 #[stable(feature = "cursor_mut_vec", since = "1.25.0")]
-impl Write for Cursor<&mut Vec<u8>> {
+impl<A> Write for Cursor<&mut Vec<u8, A>>
+where
+    A: Allocator,
+{
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         vec_write(&mut self.pos, self.inner, buf)
     }
@@ -483,7 +493,10 @@ impl Write for Cursor<&mut Vec<u8>> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl Write for Cursor<Vec<u8>> {
+impl<A> Write for Cursor<Vec<u8, A>>
+where
+    A: Allocator,
+{
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         vec_write(&mut self.pos, &mut self.inner, buf)
     }
@@ -504,7 +517,10 @@ impl Write for Cursor<Vec<u8>> {
 }
 
 #[stable(feature = "cursor_box_slice", since = "1.5.0")]
-impl Write for Cursor<Box<[u8]>> {
+impl<A> Write for Cursor<Box<[u8], A>>
+where
+    A: Allocator,
+{
     #[inline]
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         slice_write(&mut self.pos, &mut self.inner, buf)