mirror of https://github.com/rust-lang/nomicon
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
50 lines
1.7 KiB
50 lines
1.7 KiB
% Insert and Remove
|
|
|
|
Something *not* provided but slice is `insert` and `remove`, so let's do those next.
|
|
|
|
Insert needs to shift all the elements at the target index to the right by one.
|
|
To do this we need to use `ptr::copy`, which is our version of C's `memmove`.
|
|
This copies some chunk of memory from one location to another, correctly handling
|
|
the case where the source and destination overlap (which will definitely happen
|
|
here).
|
|
|
|
If we insert at index `i`, we want to shift the `[i .. len]` to `[i+1 .. len+1]`
|
|
using the *old* len.
|
|
|
|
```rust
|
|
pub fn insert(&mut self, index: usize, elem: T) {
|
|
// Note: `<=` because it's valid to insert after everything
|
|
// which would be equivalent to push.
|
|
assert!(index <= self.len, "index out of bounds");
|
|
if self.cap == self.len { self.grow(); }
|
|
|
|
unsafe {
|
|
if index < self.len {
|
|
// ptr::copy(src, dest, len): "copy from source to dest len elems"
|
|
ptr::copy(self.ptr.offset(index as isize),
|
|
self.ptr.offset(index as isize + 1),
|
|
len - index);
|
|
}
|
|
ptr::write(self.ptr.offset(index as isize), elem);
|
|
self.len += 1;
|
|
}
|
|
}
|
|
```
|
|
|
|
Remove behaves in the opposite manner. We need to shift all the elements from
|
|
`[i+1 .. len + 1]` to `[i .. len]` using the *new* len.
|
|
|
|
```rust
|
|
pub fn remove(&mut self, index: usize) -> T {
|
|
// Note: `<` because it's *not* valid to remove after everything
|
|
assert!(index < self.len, "index out of bounds");
|
|
unsafe {
|
|
self.len -= 1;
|
|
let result = ptr::read(self.ptr.offset(index as isize));
|
|
ptr::copy(self.ptr.offset(index as isize + 1),
|
|
self.ptr.offset(index as isize),
|
|
len - index);
|
|
result
|
|
}
|
|
}
|
|
``` |