[Development] Suggested addition to wiki.qt.io/Coding_Conventions

[Konstantin Ritt]

I guess this came from QSslEllipticCurve.
+1 for not doing that until it really affects release build [with
non-broken compilers].

Regards,
Konstantin

2015-05-13 17:45 GMT+04:00 Matthew Woehlke <mw_triad at users.sourceforge.net>:

> On 2015-05-13 04:25, Marc Mutz wrote:
> > Hi,
> >
> > I'd like to suggest the following addition to the Qt Coding Conventions:
> >
> > === Exporting Classes ===
> >
> > Export polymorphic classes as a whole:
> >
> > <code>
> >   class Q_LIB_EXPORT QMyWidget : public QWidget
> >   { ...
> > </code>
> >
> > But don't export non-polymorphic classes that way. Instead, only export
> the
> > following non-inline methods.
> >
> > * public
> > * protected
> > * private, if called from inline functions (now or in the past)
> >
> > Rationale: On Windows, symbols from a DLL that don't have inline linkage
> > (templates or inline functions have inline linkage) need to be exported
> for
> > clients to link against them, This is what the <tt>Q_*_EXPORT</tt>
> macros are
> > for. On some Unix systems, the macros map to a similar mechanism that
> > <em>hides</em> symbols not exported that way, positively affecting
> startup
> > performance and library size.
> >
> > But exporting the whole class, while convenient, has several drawback:
> >
> > * it exports symbols that don't need exporting:
> > ** private methods never called from user code
> > ** methods of private nested structs and classes
>
> Many Qt classes have corresponding Private (PIMPL) classes. Private
> methods would hopefully be few and far between.
>
> Is it possible to override the export decoration for things like this
> that should *not* be exported?
>
> > ** inline methods
> > * exporting inline methods makes MSVC call the library implementation in
> debug
> > builds
>
> That's a feature. There are reasons why debug builds don't inline
> (mostly because it makes stack traces unreliable).
>
> > ** a copy of the function is placed in the library even though the
> library
> > itself may never use it
>
> What if I need to take the address of an inline method (e.g. to use it
> as a functor argument)?
>
> > ** exported inline functions can no longer be removed
>
> They can't anyway, as this would be both an API and ABI break; see
> previous point.
>
> --
> Matthew
>
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