Why is there a difference between Super-Space and other shortcuts?

Question

By default the application launcher is called with Super + Space and Alt + F2. (It can be changed.)

But there is a difference; after showing the Applications launcher, the Super + Space shortcut also hides it if pressed again; Alt + F2 doesn't do that.

And neither do other shortcuts:

The same difference is present if the default shortcuts are changed as indicated in the answers to the linked question: the launcher is shown but not hidden with just the Super key (unlike in Ubuntu Unity). That is my main reason against giving up the default Super + Space shortcut in favor of just Super on elementary OS.

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What is special behind Super + Space ?

Answer 1

The difference is that Super+Space is hardcoded right in to Slingshot. It does not check system settings for different keybindings.

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I grabbed the latest source code and had a look for the word "Super". I came across this in one of the source files:

// Handle super+space when the user is typing in the search entry 
private bool search_entry_key_press (Gdk.EventKey event) { 
    if ((event.keyval == Gdk.Key.space) && ((event.state & Gdk.ModifierType.SUPER_MASK) != 0)) { 
        hide (); 
        return true; 
    }   

    switch (event.keyval) { 
        case Gdk.Key.Tab: 
            // context view is disabled until we get plugins that are actually 
            // useful with a context 
            // search_view.toggle_context (!search_view.in_context_view); 
            return true; 
    }   

    return false; 
}

You can see that it is hardcoded to only check for Super+Space in order to hide.

The source code can be found at Revision 558, Line 413.