tests/ui/const-generics/type-dependent/issue-71805.rs

   1 // run-pass
   2 use std::mem::MaybeUninit;
   3
   4 trait CollectSlice<'a>: Iterator {
   5     fn inner_array<const N: usize>(&mut self) -> [Self::Item; N];
   6
   7     fn collect_array<const N: usize>(&mut self) -> [Self::Item; N] {
   8         let result = self.inner_array();
   9         assert!(self.next().is_none());
  10         result
  11     }
  12 }
  13
  14 impl<'a, I: ?Sized> CollectSlice<'a> for I
  15 where
  16     I: Iterator,
  17 {
  18     fn inner_array<const N: usize>(&mut self) -> [Self::Item; N] {
  19         let mut result: [MaybeUninit<Self::Item>; N] =
  20             unsafe { MaybeUninit::uninit().assume_init() };
  21
  22         let mut count = 0;
  23         for (dest, item) in result.iter_mut().zip(self) {
  24             *dest = MaybeUninit::new(item);
  25             count += 1;
  26         }
  27
  28         assert_eq!(N, count);
  29
  30         let temp_ptr: *const [MaybeUninit<Self::Item>; N] = &result;
  31         unsafe { std::ptr::read(temp_ptr as *const [Self::Item; N]) }
  32     }
  33 }
  34
  35 fn main() {
  36     let mut foos = [0u64; 9].iter().cloned();
  37     let _bar: [u64; 9] = foos.collect_array::<9_usize>();
  38 }