See also https://github.com/golang/go/issues/29982. It gets more
interesting towards the bottom, but the proposal is on hold.
Be nice to release it again though. I do favor it.
-rob
On Tue, Oct 26, 2021 at 8:48 AM Ian Lance Taylor <i...@golang.org> wrote:
>
> On Sun, Oct 24, 2021 at 4:45 PM jlfo...@berkeley.edu
> <jlforr...@berkeley.edu> wrote:
> >
> > But, I still have some questions about the responses. First, I think the
> > expected value of len(struct) should be its size, in bytes,
> > like with a string. Are there any examples of problems this would cause?
>
> I believe that that would be surprising. For example,
> unsafe.Sizeof("") == 16 (on a 64-bit platform) but len("") == 0. len
> always returns the number of elements contained in some aggregate
> type, not the size of a value of that type. So if we supported len on
> a struct type, I think the most natural value to return would be the
> number of fields, not the total size of the struct. But of course
> that isn't very useful in practice, so we simply don't support len on
> a struct type.
>
> > I don't understand why this has to be
> > unsafe. (It could even be done at compile time). I also don't understand
> > the comment about recursive calls. Since it's possible
> > to assign one structure to another I would think that the structure length
> > is known. Since I'm new to Go I'm probably
> > not aware of the finer points that would make this not so.
>
> The size of a struct type is indeed known at compile time, and
> unsafe.Sizeof applied to a struct type returns a constant that is the
> size of the struct. You're right in that this does not really have to
> be in unsafe (and you can get the same value using the reflect package
> without using unsafe, although the result will be not technically be a
> constant--it will always be the same value, but you can't use it to
> set the size of an array). unsafe.Sizeof is in unsafe mainly for
> historical reasons and because there wasn't anywhere else natural to
> put it.
>
> Ian
>
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