Your proposal seems like an unnecessary half measure to me. If you want to go fully ergonomic, you can expose:

    pub unsafe fn qsort<E, C: FnMut(&E, &E) -> core::cmp::Ordering>(elements: &mut [E], mut comp: C)

In rust as currently stands: https://play.rust-lang.org/?version=stable&mode=debug&editio...

On the other hand, both this wrapper and yours are counterproductive if the element size is dynamic (e.g. perhaps you're dealing with some nonsense like:)

    struct ITableColumn {
        virtual ~ITableColumn() {}
        virtual void* base() = 0;
        virtual size_t stride() const = 0;
        virtual int (*)(void*, void*) get_comparison_func() const = 0;
    };