[PyQt] Patch fixing some const issues

[oliver]

Without seeing the code this may be Irrelevant but one thing I remember
about autopointer is that it has move semantics. So for "a=b" with both
being autopointer, causes b to become an autopointer to null. B can be an
autopointer to const but cannot be a const autopointer.

On Fri, Aug 11, 2017, 12:22 Shaheed Haque, <srhaque at theiet.org> wrote:

> On 11 August 2017 at 16:55, Phil Thompson <phil at riverbankcomputing.com>
> wrote:
>
>> On 11 Aug 2017, at 4:37 pm, Shaheed Haque <srhaque at theiet.org> wrote:
>> >
>> >
>> >
>> > On 11 August 2017 at 16:02, Phil Thompson <phil at riverbankcomputing.com>
>> wrote:
>> > On 11 Aug 2017, at 1:47 pm, Shaheed Haque <srhaque at theiet.org> wrote:
>> > >
>> > > Hi,
>> > >
>> > > Based on 4.19.4.dev1708081632, I see some issues with the emitted
>> code involving casts. There are several cases, but here is one example that
>> illustrates the issue:
>> > >
>> > > ===  4.19.4.dev1708081632 output ===
>> > > static void assign_std_auto_ptr_0100GpgME_EditInteractor(void
>> *sipDst, SIP_SSIZE_T sipDstIdx, const void *sipSrc)
>> > > {
>> > >     reinterpret_cast< ::std::auto_ptr< ::GpgME::EditInteractor>
>> *>(sipDst)[sipDstIdx] = *reinterpret_cast<const ::std::auto_ptr<
>> ::GpgME::EditInteractor> *>(sipSrc);
>> > > }
>> > > ==============================
>> > >
>> > > The above won't compile with errors boiling down, IIUC, to the fact
>> that the RHS has type "const something", and this is not compatible with
>> the LHS which has type "something" without the const. Now, I'll confess
>> that I'm a bit rusty on some of this, but I think the correct fix is to
>> cast away the constness of sipSrc earlier, like this:
>> > >
>> > > === patched version ===
>> > > static void assign_std_auto_ptr_0100GpgME_EditInteractor(void
>> *sipDst, SIP_SSIZE_T sipDstIdx, const void *sipSrc)
>> > > {
>> > >     reinterpret_cast< ::std::auto_ptr< ::GpgME::EditInteractor>
>> *>(sipDst)[sipDstIdx] = *reinterpret_cast< ::std::auto_ptr<
>> ::GpgME::EditInteractor> *>(const_cast<void *>(sipSrc));
>> > > }
>> > > ===================
>> > >
>> > > Now, the LHS and the RHS match, and the compiler is happy. There are
>> 4 similar cases in gencode.c which I patched, as below. This patch also
>> includes my diffs for the static_cast<int>s from
>> https://www.riverbankcomputing.com/pipermail/pyqt/2017-August/039494.html
>> .
>> > >
>> > > (There is also one slightly different usage of reinterpret_cast<const
>> ...> but I am not sure if that is implicated or not).
>> >
>> > I don't see why the RHS breaks the constness. Is std::auto_ptr doing
>> something out of the ordinary?
>> >
>> > As I hinted, I'm well outside my comfort zone here, so take anything
>> say with a pinch of salt. That said...
>> >
>> > It *might* well be auto_ptr-related, but I'm not sure, because the
>> second paragraph on page http://en.cppreference.com/w/cpp/memory/auto_ptr
>> seems to suggest that the RHS is being modified by the assignment (but that
>> seems astonishing to me, so perhaps I am misreading it?). It is also true
>> that all of the other templated types I am trying to support work fine in
>> this regard.
>> >
>> > At any rate, the voluminous errors that result all seem to point to the
>> assignment itself being bad, and to my simple-minded thinking, the problem
>> is more that with the original formulation, the RHS is a const-qualified
>> type, while the LHS is not.
>>
>> Yes but the expression is making a copy of the object on the RHS so the
>> mis-match shouldn't make a difference.
>>
>
> My reading is that the documentation saying that the RHS is changed by the
> assignment, and that the const is interfering with that!
>
>
>> Phil
>
>
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-- 
Oliver
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