Method from_trusted_len_iter

arrow-buffer/src/buffer/mutable.rs:958–982

(
        iterator: I,
    )

    // 2. `from_trusted_len_iter` is faster.
    #[inline]
    pub unsafe fn from_trusted_len_iter<T: ArrowNativeType, I: Iterator<Item = T>>(
        iterator: I,
    ) -> Self {
        let item_size = std::mem::size_of::<T>();
        let (_, upper) = iterator.size_hint();
        let upper = upper.expect("from_trusted_len_iter requires an upper limit");
        let len = upper * item_size;

        let mut buffer = MutableBuffer::new(len);

        let mut dst = buffer.data.as_ptr();
        for item in iterator {
            // note how there is no reserve here (compared with `extend_from_iter`)
            let src = item.to_byte_slice().as_ptr();
            unsafe { std::ptr::copy_nonoverlapping(src, dst, item_size) };
            dst = unsafe { dst.add(item_size) };
        }
        assert_eq!(
            unsafe { dst.offset_from(buffer.data.as_ptr()) } as usize,
            len,
            "Trusted iterator length was not accurately reported"
        );
        buffer.len = len;
        buffer
    }

    /// Creates a [`MutableBuffer`] from a boolean [`Iterator`] with a trusted (upper) length.
    /// # use arrow_buffer::buffer::MutableBuffer;