diff options
| -rw-r--r-- | src/libcollections/vec.rs | 29 |
1 files changed, 19 insertions, 10 deletions
diff --git a/src/libcollections/vec.rs b/src/libcollections/vec.rs index f294dd3c3e0..74b5b2cae0e 100644 --- a/src/libcollections/vec.rs +++ b/src/libcollections/vec.rs @@ -1383,7 +1383,7 @@ impl<T> ops::DerefMut for Vec<T> { #[stable(feature = "rust1", since = "1.0.0")] impl<T> FromIterator<T> for Vec<T> { #[inline] - fn from_iter<I:Iterator<Item=T>>(iterator: I) -> Vec<T> { + fn from_iter<I:Iterator<Item=T>>(mut iterator: I) -> Vec<T> { let (lower, _) = iterator.size_hint(); let mut vector = Vec::with_capacity(lower); @@ -1393,13 +1393,20 @@ impl<T> FromIterator<T> for Vec<T> { // vector.push(item); // } // - // This equivalent crucially runs the iterator precisely once. The - // optimization below (eliding bound/growth checks) means that we - // actually run the iterator twice. To ensure the "moral equivalent" we - // do a `fuse()` operation to ensure that the iterator continues to - // return `None` after seeing the first `None`. - let mut i = iterator.fuse(); - for element in i.by_ref().take(vector.capacity()) { + // This equivalent crucially runs the iterator precisely once. Below we + // actually in theory run the iterator twice (one without bounds checks + // and one with). To achieve the "moral equivalent", we use the `if` + // statement below to break out early. + // + // If the first loop has terminated, then we have one of two conditions. + // + // 1. The underlying iterator returned `None`. In this case we are + // guaranteed that less than `vector.capacity()` elements have been + // returned, so we break out early. + // 2. The underlying iterator yielded `vector.capacity()` elements and + // has not yielded `None` yet. In this case we run the iterator to + // its end below. + for element in iterator.by_ref().take(vector.capacity()) { let len = vector.len(); unsafe { ptr::write(vector.get_unchecked_mut(len), element); @@ -1407,8 +1414,10 @@ impl<T> FromIterator<T> for Vec<T> { } } - for element in i { - vector.push(element) + if vector.len() == vector.capacity() { + for element in iterator { + vector.push(element); + } } vector } |