[Lldb-commits] [lldb] r222186 - Fix override/virtual warnings.
Zachary Turner
zturner at google.com
Mon Nov 17 17:54:43 PST 2014
It's true you have to remember whether you're in the base class, but as you
deduced, that's pretty much the point. FWIW I switched all of
ProcessWindows over to using it just a day ago, because I found some dead
code that occurred due to not using it, which this would have found.
Apparently process plugins used to have plugin logging and plugin commands,
because ProcessLinux and ProcessWindows had stub methods like
EnablePluginLogging and ExecutePluginCommand, but these methods were
nowhere to be found in base classes. So I guess at some point they were
deleted, but since virtual both declares a new virtual method and overrides
an existing one, this dead code was never detected.
This isn't quite as serious as introducing an actual bug, but either way,
we can all agree that dead code sucks.
Since the virtual keyword is optional but harmless on an override, we could
always adopt the policy of requiring the "virtual" keyword on an override,
which should address your concern of having to look in two places. This
way you can still simply look at the beginning to see if a method is
virtual or not, and override is just a little syntatic sugar on the end to
get the compiler to generate an error when you actually make an error.
On Mon Nov 17 2014 at 5:36:22 PM <jingham at apple.com> wrote:
> Override seems kind of gross to me. I can't use it on base class
> functions. If I just use override I get
>
> override.cpp:3:22: error: only virtual member functions can be marked
> 'override'
> int DoSomething () override;
>
> and if I put both I get:
>
> override.cpp:3:15: error: 'DoSomething' marked 'override' but does not
> override any member functions
> virtual int DoSomething () override;
> ^
> Now I have to remember whether I'm in the base class for this method or
> not, and I have to look in two places in the declaration (one after lots of
> noise) to see whether the method is actually virtual or not.
>
> It's kinda nice that it tells me if I got a method a little wrong, but I
> wonder whether that "at the time I change method names" convenience is
> worth the more common reading through code annoyance. I vote not to use
> it, though it's not a strong vote. If we are going to use it we should go
> through and make its use consistent otherwise we'll keep getting errors
> where people copy from the base class and forget to switch all the
> "virtual" on the LHS to "override" on the RHS...
>
> Jim
>
>
> > On Nov 17, 2014, at 5:28 PM, Zachary Turner <zturner at google.com> wrote:
> >
> > override implies virtual and is a strict superset of virtual, so there's
> nothing inherently wrong with "mixing" them. The advantage of override is
> that it will cause the compiler to error if, for example, you delete a
> virtual method from a base class (or change the signature), but forget to
> make a corresponding change in derived implementations.
> >
> > For example, if you have
> >
> > class A
> > {
> > public:
> > virtual void Foo();
> > };
> >
> > class B : public A
> > {
> > public:
> > virtual void Foo();
> > };
> >
> > this is all fine. If someone goes and changes A to the following:
> >
> > class A
> > {
> > public:
> > virtual void Foo(int x);
> > };
> >
> > This will continue to compile no problem, and not alert the user to the
> fact that there is now a bug in the code. On the other hand, if the
> original implementation of B had been like this:
> >
> > class B : public A
> > {
> > public:
> > virtual void Foo() override; // keyword "virtual" is optional here
> > };
> >
> > then when the change was made to A, B would generate a compiler error
> that there was no appropriate method to override.
> >
> > As far as deciding to switch to override, I propose we decide that right
> now :) There's no advantage to not doing so, since it is a strict
> superset of virtual, and surfaces a common source of programmer error as a
> compiler error.
> >
> > On Mon Nov 17 2014 at 4:43:31 PM <jingham at apple.com> wrote:
> > As I understand it, mixing override & virtual is a recipe for
> confusion... We currently use virtual, and not override. At some point we
> can talk about switching over to using override everywhere, but I don't
> think we are at that point.
> >
> > So in this case your patch is incorrect, and the "virtual" should go
> back in. And then until we decide to switch to using override, can you
> turn off whatever warning is causing you to (as I understand it)
> incorrectly remove these "virtual" markers?
> >
> > Jim
> >
> >
> > > On Nov 17, 2014, at 3:14 PM, Eric Christopher <echristo at gmail.com>
> wrote:
> > >
> > > It's fine as virtual, but you're overriding a method and not marking
> it as override. You don't need to write both down (you could, but it's a
> nop) as override only works on virtual functions.
> > >
> > > -eric
> > >
> > > On Mon Nov 17 2014 at 3:07:27 PM <jingham at apple.com> wrote:
> > > I'm sure I'm missing something obvious, but I don't understand what
> this warning you are fixing is supposed to be telling you about. The
> inheritance hierarchy is:
> > >
> > > PlatformDarwin<--PlatformPOSIX<--Platform
> > >
> > > Platform.h defines:
> > >
> > > virtual Error
> > > ResolveExecutable (const FileSpec &exe_file,
> > > const ArchSpec &arch,
> > > lldb::ModuleSP &module_sp,
> > > const FileSpecList
> *module_search_paths_ptr);
> > >
> > >
> > > Then PlatformPosix.h doesn't override ResolveExecutable, and finally,
> PlatformDarwin has:
> > >
> > > virtual lldb_private::Error
> > > ResolveExecutable (const lldb_private::FileSpec &exe_file,
> > > const lldb_private::ArchSpec &arch,
> > > lldb::ModuleSP &module_sp,
> > > const lldb_private::FileSpecList
> *module_search_paths_ptr);
> > >
> > >
> > > Why is it wrong for PlatformDarwin to define this method as virtual?
> > >
> > > Jim
> > >
> > >
> > >
> > > > On Nov 17, 2014, at 2:55 PM, Eric Christopher <echristo at gmail.com>
> wrote:
> > > >
> > > > Author: echristo
> > > > Date: Mon Nov 17 16:55:13 2014
> > > > New Revision: 222186
> > > >
> > > > URL: http://llvm.org/viewvc/llvm-project?rev=222186&view=rev
> > > > Log:
> > > > Fix override/virtual warnings.
> > > >
> > > > Modified:
> > > > lldb/trunk/source/Plugins/Platform/MacOSX/PlatformDarwin.h
> > > >
> > > > Modified: lldb/trunk/source/Plugins/Platform/MacOSX/PlatformDarwin.h
> > > > URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/source/
> Plugins/Platform/MacOSX/PlatformDarwin.h?rev=222186&
> r1=222185&r2=222186&view=diff
> > > > ============================================================
> ==================
> > > > --- lldb/trunk/source/Plugins/Platform/MacOSX/PlatformDarwin.h
> (original)
> > > > +++ lldb/trunk/source/Plugins/Platform/MacOSX/PlatformDarwin.h Mon
> Nov 17 16:55:13 2014
> > > > @@ -27,57 +27,58 @@ public:
> > > > //------------------------------------------------------------
> > > > // lldb_private::Platform functions
> > > > //------------------------------------------------------------
> > > > - virtual lldb_private::Error
> > > > + lldb_private::Error
> > > > ResolveExecutable (const lldb_private::ModuleSpec &module_spec,
> > > > lldb::ModuleSP &module_sp,
> > > > const lldb_private::FileSpecList
> *module_search_paths_ptr) override;
> > > >
> > > > - virtual lldb_private::Error
> > > > + lldb_private::Error
> > > > ResolveSymbolFile (lldb_private::Target &target,
> > > > const lldb_private::ModuleSpec &sym_spec,
> > > > - lldb_private::FileSpec &sym_file);
> > > > + lldb_private::FileSpec &sym_file) override;
> > > >
> > > > lldb_private::FileSpecList
> > > > LocateExecutableScriptingResources (lldb_private::Target
> *target,
> > > > lldb_private::Module &module,
> > > > - lldb_private::Stream*
> feedback_stream);
> > > > + lldb_private::Stream*
> feedback_stream) override;
> > > >
> > > > - virtual lldb_private::Error
> > > > + lldb_private::Error
> > > > GetSharedModule (const lldb_private::ModuleSpec &module_spec,
> > > > lldb::ModuleSP &module_sp,
> > > > const lldb_private::FileSpecList
> *module_search_paths_ptr,
> > > > lldb::ModuleSP *old_module_sp_ptr,
> > > > - bool *did_create_ptr);
> > > > + bool *did_create_ptr) override;
> > > >
> > > > - virtual size_t
> > > > + size_t
> > > > GetSoftwareBreakpointTrapOpcode (lldb_private::Target &target,
> > > > - lldb_private::BreakpointSite
> *bp_site);
> > > > + lldb_private::BreakpointSite
> *bp_site) override;
> > > >
> > > > - virtual bool
> > > > + bool
> > > > GetProcessInfo (lldb::pid_t pid,
> > > > - lldb_private::ProcessInstanceInfo &proc_info);
> > > > + lldb_private::ProcessInstanceInfo &proc_info)
> override;
> > > >
> > > > - virtual lldb::BreakpointSP
> > > > - SetThreadCreationBreakpoint (lldb_private::Target &target);
> > > > + lldb::BreakpointSP
> > > > + SetThreadCreationBreakpoint (lldb_private::Target &target)
> override;
> > > >
> > > > - virtual uint32_t
> > > > + uint32_t
> > > > FindProcesses (const lldb_private::ProcessInstanceInfoMatch
> &match_info,
> > > > - lldb_private::ProcessInstanceInfoList
> &process_infos);
> > > > -
> > > > - virtual bool
> > > > - ModuleIsExcludedForNonModuleSpecificSearches
> (lldb_private::Target &target, const lldb::ModuleSP &module_sp);
> > > > -
> > > > + lldb_private::ProcessInstanceInfoList
> &process_infos) override;
> > > > +
> > > > + bool
> > > > + ModuleIsExcludedForNonModuleSpecificSearches(lldb_private::Target
> &target,
> > > > + const lldb::ModuleSP
> &module_sp) override;
> > > > +
> > > > bool
> > > > ARMGetSupportedArchitectureAtIndex (uint32_t idx,
> lldb_private::ArchSpec &arch);
> > > >
> > > > bool
> > > > x86GetSupportedArchitectureAtIndex (uint32_t idx,
> lldb_private::ArchSpec &arch);
> > > >
> > > > - virtual int32_t
> > > > - GetResumeCountForLaunchInfo (lldb_private::ProcessLaunchInfo
> &launch_info);
> > > > + int32_t
> > > > + GetResumeCountForLaunchInfo (lldb_private::ProcessLaunchInfo
> &launch_info) override;
> > > >
> > > > - virtual void
> > > > - CalculateTrapHandlerSymbolNames ();
> > > > + void
> > > > + CalculateTrapHandlerSymbolNames () override;
> > > >
> > > > protected:
> > > >
> > > >
> > > >
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> > >
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