Deriving from Pango::Layout

[Phil Wolff <adiabat centurylink net>]

#include <gtkmm.h>

class CTextBuffer : public Gtk::TextBuffer
{
public:
    static Glib::RefPtr<CTextBuffer > create ( Gtk::TextView* );
    virtual ~CTextBuffer () {}
private:
    explicit CTextBuffer ( Gtk::TextView* );
    Gtk::TextView* m_pTextView;
};
//==================================
Glib::RefPtr<CTextBuffer > CTextBuffer::create ( Gtk::TextView* pView )
{
    return Glib::RefPtr<CTextBuffer > ( new CTextBuffer ( pView ) );
}

CTextBuffer::CTextBuffer ( Gtk::TextView* pView )
{
    m_pTextView = pView;
}

The example above compiles with no errors. However when I try it with 
Pango::Layout in place of Gtk::TextBuffer:

#include <gtkmm.h>
#include <pangomm.h>

class CLayout : public Pango::Layout
{
public:
    static Glib::RefPtr<CLayout > create ( const 
Glib::RefPtr<Pango::Context >& );
    virtual ~CLayout () {}
private:
    explicit CLayout ( const Glib::RefPtr<Pango::Context >& );
    Glib::RefPtr<Pango::Context > m_refContext;
};
//==================================
Glib::RefPtr<CLayout > CLayout::create ( const 
Glib::RefPtr<Pango::Context >& context )
{
    return Glib::RefPtr<CLayout > ( new CLayout ( context ) );
}

CLayout::CLayout ( const Glib::RefPtr<Pango::Context >& context )
{
    m_refContext = context;
}

pl.cc: In constructor ‘CLayout::CLayout(const 
Glib::RefPtr<Pango::Context>&)’:
pl.cc:20:65: error: no matching function for call to 
‘Pango::Layout::Layout()’
 CLayout::CLayout ( const Glib::RefPtr<Pango::Context >& context )
                                                                 ^
In file included from /usr/include/gtkmm-3.0/gtkmm/widget.h:32:0,
                 from /usr/include/gtkmm-3.0/gtkmm/action.h:31,
                 from /usr/include/gtkmm-3.0/gtkmm/toggleaction.h:27,
                 from /usr/include/gtkmm-3.0/gtkmm.h:95,
                 from pl.cc:1:
/usr/include/pangomm-1.4/pangomm/layout.h:259:12: note: candidate: 
Pango::Layout::Layout(const Glib::RefPtr<Pango::Context>&)
   explicit Layout(const Glib::RefPtr<Context>& context);
            ^~~~~~
/usr/include/pangomm-1.4/pangomm/layout.h:259:12: note:   candidate 
expects 1 argument, 0 provided

Can someone give me a clue as to what I'm failing to see?