General performance question

[Jonas Platte <jonasplatte myopera com>]

Hello, I've got a simple question: In gtkmm, when I want to set a 
boolean property of any object, like a widget, and I don't know it's 
current state, should I first check if the state isn't how I want it to 
be, or should I always call set? For example, in the case I want a 
widget to get insensitive, would I write:

    if(widget.get_sensitive()) widget.set_sensitive(false);

or only

    widget.set_sensitive(false);

And if it doesn't have a significant influence on the performance, which 
one would you consider the better style?

Thanks,
Jonas