On Wed, Jun 23, 2021 at 12:22 PM Richard Sandiford <richard.sandif...@arm.com> wrote: > > Richard Biener <richard.guent...@gmail.com> writes: > > On Wed, Jun 23, 2021 at 7:23 AM Trevor Saunders <tbsau...@tbsaunde.org> > > wrote: > >> > >> On Tue, Jun 22, 2021 at 02:01:24PM -0600, Martin Sebor wrote: > >> > On 6/21/21 1:15 AM, Richard Biener wrote: > > [...] > >> > > > >> > > But maybe I'm misunderstanding C++ too much :/ > >> > > > >> > > Well, I guess b) from above means auto_vec<> passing to > >> > > vec<> taking functions will need changes? > >> > > >> > Converting an auto_vec object to a vec slices off its data members. > >> > The auto_vec<T, 0> specialization has no data members so that's not > >> > a bug in and of itself, but auto_vec<T, N> does have data members > >> > so that would be a bug. The risk is not just passing it to > >> > functions by value but also returning it. That risk was made > >> > worse by the addition of the move ctor. > >> > >> I would agree that the conversion from auto_vec<> to vec<> is > >> questionable, and should get some work at some point, perhaps just > >> passingauto_vec references is good enough, or perhaps there is value in > >> some const_vec view to avoid having to rely on optimizations, I'm not > >> sure without looking more at the usage. > > > > We do need to be able to provide APIs that work with both auto_vec<> > > and vec<>, I agree that those currently taking a vec<> by value are > > fragile (and we've had bugs there before), but I'm not ready to say > > that changing them all to [const] vec<>& is OK. The alternative > > would be passing a const_vec<> by value, passing that along to > > const vec<>& APIs should be valid then (I can see quite some API > > boundary cleanups being necessary here ...). > > FWIW, as far as const_vec<> goes, we already have array_slice, which is > mostly a version of std::span. (The only real reason for not using > std::span itself is that it requires a later version of C++.) > > Taking those as arguments has the advantage that we can pass normal > arrays as well.
It's not really a "const" thing it seems though it certainly would not expose any API that would reallocate the vector (which is the problematic part of passing vec<> by value, not necessarily changing elements in-place). Since array_slice doesn't inherit most of the vec<> API transforming an API from vec<> to array_slice<> will be also quite some work. But I agree it might be useful for generic API stuff. Richard. > Thanks, > Richard
