[PyQt] Patch fixing some const issues

[Shaheed Haque]

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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