1 // run-pass
2 // Test that an `&mut self` method, when invoked on a place whose
3 // type is `&mut [u8]`, passes in a pointer to the place and not a
4 // temporary. Issue #19147.
5
6 use std::slice;
7 use std::cmp;
8
9 trait MyWriter {
my_write(&mut self, buf: &[u8]) -> Result<(), ()>10 fn my_write(&mut self, buf: &[u8]) -> Result<(), ()>;
11 }
12
13 impl<'a> MyWriter for &'a mut [u8] {
my_write(&mut self, buf: &[u8]) -> Result<(), ()>14 fn my_write(&mut self, buf: &[u8]) -> Result<(), ()> {
15 let amt = cmp::min(self.len(), buf.len());
16 self[..amt].clone_from_slice(&buf[..amt]);
17
18 let write_len = buf.len();
19 unsafe {
20 *self = slice::from_raw_parts_mut(
21 self.as_mut_ptr().add(write_len),
22 self.len() - write_len
23 );
24 }
25
26 Ok(())
27 }
28 }
29
main()30 fn main() {
31 let mut buf = [0; 6];
32
33 {
34 let mut writer: &mut [_] = &mut buf;
35 writer.my_write(&[0, 1, 2]).unwrap();
36 writer.my_write(&[3, 4, 5]).unwrap();
37 }
38
39 // If `my_write` is not modifying `buf` in place, then we will
40 // wind up with `[3, 4, 5, 0, 0, 0]` because the first call to
41 // `my_write()` doesn't update the starting point for the write.
42
43 assert_eq!(buf, [0, 1, 2, 3, 4, 5]);
44 }
45