Re: [lmi] [lmi-commits] master a67848a 1/3: Use 'new(wx)' to allocate memory that will be freed by wx

[Greg Chicares]

On 2/8/21 11:30 AM, Vadim Zeitlin wrote:
> On Sun, 7 Feb 2021 23:17:08 +0000 Greg Chicares <gchicares@sbcglobal.net> 
> wrote:
[...]
> GC> Would we write
> GC>   std::unique_ptr<InputSequenceEntry> z = new(wx) InputSequenceEntry(...);
> GC> because there's no make_unique(wx) that would delegate to new(wx)?
> 
>  I could be wrong, but I thought we only need to use new(wx) for the
> pointers deleted by wxWidgets. And normally this is the case for all window
> pointers that we create in lmi code, which is why we use new(wx) for all of
> them. However in this particular case we want to delete the window
> ourselves, so it won't be deleted by wxWidgets and hence there is no need
> for new(wx) and we can just write
> 
>       auto const z = std::make_unique<InputSequenceEntry>(...);

Should it be easy to write that in a way that compiles? I tried:

diff --git a/skeleton.cpp b/skeleton.cpp
index 267582eba..b37aa3fbf 100644
--- a/skeleton.cpp
+++ b/skeleton.cpp
@@ -1081,7 +1081,8 @@ void 
Skeleton::UponTestFloatingPointEnvironment(wxCommandEvent&)
 
 void Skeleton::UponTestPasting(wxCommandEvent&)
 {
-    InputSequenceEntry* z = new(wx) InputSequenceEntry(frame_, wxID_ANY, 
"Testing...");
+    auto const z = std::make_unique<InputSequenceEntry>
+        (InputSequenceEntry(frame_, wxID_ANY, "Testing..."));
     wxTextCtrl& t = z->text_ctrl();
 
     ClipboardEx::SetText("1\r\n2\r\n3\r\n");
@@ -1100,7 +1101,6 @@ void Skeleton::UponTestPasting(wxCommandEvent&)
         warning() << "'X;Y;Z;' != '" << t.GetValue() << "'" << LMI_FLUSH;
         }
 
-    z->Destroy();
     status() << "Pasting test finished." << std::flush;
 }
 
but gcc complains:

/usr/lib/gcc/i686-w64-mingw32/8.3-win32/include/c++/bits/unique_ptr.h: In 
instantiation of ‘typename std::_MakeUniq<_Tp>::__single_object 
std::make_unique(_Args&& ...) [with _Tp = InputSequenceEntry; _Args = 
{InputSequenceEntry}; typename std::_MakeUniq<_Tp>::__single_object = 
std::unique_ptr<InputSequenceEntry, std::default_delete<InputSequenceEntry> >]’:
/opt/lmi/src/lmi/skeleton.cpp:1085:60:   required from here
/usr/lib/gcc/i686-w64-mingw32/8.3-win32/include/c++/bits/unique_ptr.h:827:30: 
error: use of deleted function ‘InputSequenceEntry::InputSequenceEntry(const 
InputSequenceEntry&)’
     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /opt/lmi/src/lmi/skeleton.cpp:61:
/opt/lmi/src/lmi/input_sequence_entry.hpp:44:5: note: declared here
     InputSequenceEntry(InputSequenceEntry const&) = delete;
     ^~~~~~~~~~~~~~~~~~

I even tried making it a shared_ptr, in the hope that that would
be less fussy, but got similar diagnostics.

Is there something unholy about class InputSequenceEntry that makes
this fail? I thought that shared_ptr<T> in particular placed no
requirements on type T other than that T::~T() mustn't throw.