Re: [sigc] Functor from variable

[Martin Schulze <martin-ml hippogriff de>]

Am 05.08.2004 20:37:45 schrieb(en) Roger Ferrer Ibáñez:
> Hello,
>
> I was just wondering if it is possible in libsigc++ to create a  
> functor
> from a variable. So you get a functor that returns the value of this
> variable and receives no parameter.
>
> I've seen there's a way to get a similar effect by binding the return  
> of
> a function of the same type to a sigc::ref of the variable. Something
> like this:

I'm not sure without trying myself, but please let me know whether the  
following code works:

 #include <sigc++/adaptors/lambda/lambda.h>
 [...]
 readValue.connect(sigc::var(data));
 [...]

Regards,

 Martin


> -- Example --
> int dummyOne()
> {
> ~  cout << "Calling " << __FUNCTION__ << endl;
> ~  return 0;
> }
>
> int main(int argc, char* argv[])
> {
> ~  int data;
> ~  sigc::signal<int> readValue;
>
> ~  readValue.connect(sigc::bind_return(&dummyOne, sigc::ref(data)));
>
> ~  data = 3;
> ~  cout << readValue() << endl;
>
> ~  data = 5;
> ~  cout << readValue() << endl;
> }
> -- End of Example --
>
> -- Output --
> Calling dummyOne
> 3
> Calling dummyOne
> 5
> -- End of Output --
>
> Is there a way to avoid the unnecessary call to dummyOne? Maybe  
> making
> inline the dummy function would reduce it (already small) impact?
>
> Something like
>
> ~  readValue.connect(sigc::var_fun(sigc::ref(data)));
>
> sigc::var_fun would create a functor that returns the type of data  
> (int)
> and receives no parameter (a 0-ary function).
>
> Thank you for your attention!
>
> --
> Roger Ferrer Ibáñez
> Correu: rofi ya com
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