[Qt-interest] Question SLOT Macro & messing with the QObject::connect method

[kent williams]

I just have the habit of turning any block of code I need to use over
and over again into a convenience function.  I'd think EVERYONE would
want to have that habit, but when I read other people's code it sure
seems like they're a lot more excited by Cut & Paste in their editor
than they are about functional decomposition as a programming
technique.

Anyway Creating menus is one of those things I do more than once, so I
made it a function.

So in my code I have something like this:

QMenu *menu = new QMenu(this); // this being the main window of the application
const char *items[] = { "First Item", "Second Item", "Third Item", 0 };
this->MakeMenu(menu, "handleMenuItems()", items);

I COULD create actions one at a time and add them to the menu, but in
this case, I just have to write 3 lines of code. Plus, if I want to
change something about how my menus are constructed, I only have to
fix the MakeMenu method, not change the code every place I make a
menu.

What it really boils down to is this: Qt defines this method for QObject:
bool QObject::connect( const QObject * sender,
                                  const char * signal,
                                  const QObject * receiver,
                                  const char * method,
                                  Qt::ConnectionType type =
Qt::AutoConnection );

But the strings for the parameter signal and method encode their type
with a prepended '1', '2', or '3'.  Now I've been programming
computers since 1983, I really have no trouble prepending a digit on
my signal/slot string.  What I was asking is this:

Is there a better way to do this that is more consistent with the
spirit of Qt, or did the Qt authors figure people would just read the
headers and hack it together the way I did?

On Thu, Feb 4, 2010 at 1:19 PM, Jefferson Bandeira <jbsilva at ufrj.br> wrote:
> I really can't see what exactly you're trying to do with that piece of code,
> are you trying to introduce Custom Slots at runtime? 'Cause i think it's not
> supported at all, if it's not this, could you clarify a bit what exactly are
> you trying to do?
>
> 2010/2/4 kent williams <nkwmailinglists at gmail.com>
>>
>> I don't think you understand what Slot does.
>>
>> #define SLOT(a) "1"#a
>>
>> # is the preprocessor 'stringify' operation.  It takes the argument
>> and turns it into a string literal. For example
>> SLOT(kickme())
>>
>> is turned by the C Preprocessor into
>>
>> "1" "kickme()"
>>
>> and since adjacent string literals are merged, it will become
>>
>> "1kickme()"
>>
>> So you can _ONLY_ use the SLOT macro at compile time.
>>
>> At runtime, say, if you want to stick a bunch of boilerplate Qt code
>> into a convenience function, you just can't use SLOT(), because
>> there's no way to go from a passed const char * parameter back to a
>> string literal to use for a SLOT parameter.  You  can fake it -- which
>> is what I do -- create a string at runtime with a literal '1'
>> prepended.
>>
>> The problem, as I see it, is that with respect to proper C++ the
>> SIGNAL/SLOT/METHOD business is stuck in the compile-time realm, even
>> the the whole POINT of Qt's Signals and Slots paradigm is that the
>> connections between signals and slots happen at runtime!
>>
>>
>> On Thu, Feb 4, 2010 at 11:17 AM, Ian Thomson <Ian.Thomson at iongeo.com>
>> wrote:
>> > Hi,
>> >
>> > kent williams wrote:
>> >>
>> >> So my question is this: is there a non-evil way to get around SLOT()
>> >> requiring a string literal instead of a char * variable?
>> >
>> > Isn't the const char* you're talking about a literal somewhere else in
>> > your
>> > program? Call SLOT() on it there.
>> >
>> >
>> > Cheers,
>> > Ian.
>> >
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>
>
>
> --
> Jefferson Bandeira
>
>
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