[PING][PATCH] define auto_vec copy ctor and assignment (PR 90904)

[Martin Sebor <msebor@gmail.com>]

Ping:

https://gcc.gnu.org/pipermail/gcc-patches/2021-April/568901.html

On 4/27/21 9:52 AM, Martin Sebor wrote:
> On 4/27/21 8:04 AM, Richard Biener wrote:
>> On Tue, Apr 27, 2021 at 3:59 PM Martin Sebor <msebor@gmail.com> wrote:
>>>
>>> On 4/27/21 1:58 AM, Richard Biener wrote:
>>>> On Tue, Apr 27, 2021 at 2:46 AM Martin Sebor via Gcc-patches
>>>> <gcc-patches@gcc.gnu.org> wrote:
>>>>>
>>>>> PR 90904 notes that auto_vec is unsafe to copy and assign because
>>>>> the class manages its own memory but doesn't define (or delete)
>>>>> either special function.  Since I first ran into the problem,
>>>>> auto_vec has grown a move ctor and move assignment from
>>>>> a dynamically-allocated vec but still no copy ctor or copy
>>>>> assignment operator.
>>>>>
>>>>> The attached patch adds the two special functions to auto_vec along
>>>>> with a few simple tests.  It makes auto_vec safe to use in containers
>>>>> that expect copyable and assignable element types and passes bootstrap
>>>>> and regression testing on x86_64-linux.
>>>>
>>>> The question is whether we want such uses to appear since those
>>>> can be quite inefficient?  Thus the option is to delete those 
>>>> operators?
>>>
>>> I would strongly prefer the generic vector class to have the properties
>>> expected of any other generic container: copyable and assignable.  If
>>> we also want another vector type with this restriction I suggest to add
>>> another "noncopyable" type and make that property explicit in its name.
>>> I can submit one in a followup patch if you think we need one.
>>
>> I'm not sure (and not strictly against the copy and assign).  Looking 
>> around
>> I see that vec<> does not do deep copying.  Making auto_vec<> do it
>> might be surprising (I added the move capability to match how vec<>
>> is used - as "reference" to a vector)
> 
> The vec base classes are special: they have no ctors at all (because
> of their use in unions).  That's something we might have to live with
> but it's not a model to follow in ordinary containers.
> 
> The auto_vec class was introduced to fill the need for a conventional
> sequence container with a ctor and dtor.  The missing copy ctor and
> assignment operators were an oversight, not a deliberate feature.
> This change fixes that oversight.
> 
> The revised patch also adds a copy ctor/assignment to the auto_vec
> primary template (that's also missing it).  In addition, it adds
> a new class called auto_vec_ncopy that disables copying and
> assignment as you prefer.  It also disables copying for
> the auto_string_vec class.
> 
> Martin