> If this produces simiarly nice code (I haven't checked yet) I'll be very happy You didn't specify what the type of `buffer` was, so I picked a `u8`. This cod

> If this produces simiarly nice code (I haven't checked yet) I'll be very happy You didn't specify what the type of `buffer` was, so I picked a `u8`. This code[1]: pub struct Thing { buffer: Vec<u8>, } impl Thing { pub fn copy(&mut self, data: &[u8]) { for (dest, &source) in self.buffer.iter_mut().zip(data) { *dest = source; } } } Produces this assembly: _ZN10playground5Thing4copy17hf523bcb10e2298f3E: .cfi_startproc pushq %rax .Ltmp0: .cfi_def_cfa_offset 16 movq 16(%rdi), %rax cmpq %rdx, %rax cmovbeq %rax, %rdx testq %rdx, %rdx je .LBB0_2 movq (%rdi), %rdi callq memcpy@PLT .LBB0_2: popq %rax retq The call to `memcpy` is what makes me happy. ---- Your `count_bits` already exists as a combination of iterator adapters (`filter`[2] and `count`[3]): a_bit_iterator.filter(|bit| bit).count() Although if you have a numeric value, I'd suggest using `count_ones`[4], which can use the `popcnt` intrinsic. If you wanted to count all the bits in an array, I'd suggest `map`[5] and `sum`[6] let p = [1u8, 2, 54, 2, 3, 6]; let result: u32 = p.iter().map(|b| b.count_ones()).sum(); If you wanted to keep the bit iterator, you could also use `flat_map`[7]. [1]: https://play.integer32.com/?gist=03f8ffbe3ade6ced4d315c8e02063f29&version=stable https://play.integer32.com/?gist=03f8ffbe3ade6ced4d315c8e020... [2]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho... [3]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.count https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho... [4]: https://doc.rust-lang.org/std/primitive.u8.html#method.count_ones https://doc.rust-lang.org/std/primitive.u8.html#method.count... [5]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.map https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho... [6]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.sum https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho... [7]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flat_map https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho...