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Auto merge of #34771 - murarth:string-insert-str, r=alexcrichton
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Add method `String::insert_str`
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bors authored Jul 22, 2016
2 parents 0d75975 + 0bcf64c commit d15e265
Showing 1 changed file with 53 additions and 9 deletions.
62 changes: 53 additions & 9 deletions src/libcollections/string.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1132,18 +1132,62 @@ impl String {
assert!(idx <= len);
assert!(self.is_char_boundary(idx));
let bits = ch.encode_utf8();
let bits = bits.as_slice();
let amt = bits.len();

unsafe {
self.insert_bytes(idx, bits.as_slice());
}
}

unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
let len = self.len();
let amt = bytes.len();
self.vec.reserve(amt);

ptr::copy(self.vec.as_ptr().offset(idx as isize),
self.vec.as_mut_ptr().offset((idx + amt) as isize),
len - idx);
ptr::copy(bytes.as_ptr(),
self.vec.as_mut_ptr().offset(idx as isize),
amt);
self.vec.set_len(len + amt);
}

/// Inserts a string into this `String` at a byte position.
///
/// This is an `O(n)` operation as it requires copying every element in the
/// buffer.
///
/// # Panics
///
/// Panics if `idx` is larger than the `String`'s length, or if it does not
/// lie on a [`char`] boundary.
///
/// [`char`]: ../../std/primitive.char.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(insert_str)]
///
/// let mut s = String::from("bar");
///
/// s.insert_str(0, "foo");
///
/// assert_eq!("foobar", s);
/// ```
#[inline]
#[unstable(feature = "insert_str",
reason = "recent addition",
issue = "0")]
pub fn insert_str(&mut self, idx: usize, string: &str) {
let len = self.len();
assert!(idx <= len);
assert!(self.is_char_boundary(idx));

unsafe {
ptr::copy(self.vec.as_ptr().offset(idx as isize),
self.vec.as_mut_ptr().offset((idx + amt) as isize),
len - idx);
ptr::copy(bits.as_ptr(),
self.vec.as_mut_ptr().offset(idx as isize),
amt);
self.vec.set_len(len + amt);
self.insert_bytes(idx, string.as_bytes());
}
}

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