[glibmm/glibmm-2-62] Property: Add const get_proxy() returning ReadOnly

[Kjell Ahlstedt <kjellahl src gnome org>]

commit eea964ac3ac6aa57fdc6f4d348fad3e94fd624de
Author: Daniel Boles <dboles src gnome org>
Date:   Mon Sep 16 14:40:35 2019 +0200

    Property: Add const get_proxy() returning ReadOnly
    
    We could only get_proxy() if non-const and with a read/write Proxy. This
    resolves that so that we can get a read-only proxy from a const Property
    (without having to construct manually from the instance/name as before).
    
    Close https://gitlab.gnome.org/GNOME/glibmm/issues/44

 glib/glibmm/property.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/glib/glibmm/property.h b/glib/glibmm/property.h
index a370d3c9..190b10c9 100644
--- a/glib/glibmm/property.h
+++ b/glib/glibmm/property.h
@@ -169,6 +169,7 @@ private:
  *   Glib::Property<bool> property_mybool;
  *   // or private, and combined with Glib::PropertyProxy<>.
  *   Glib::PropertyProxy<int> property_myint() { return property_myint_.get_proxy(); }
+ *   Glib::PropertyProxy_ReadOnly<int> property_myint() const { return property_myint_.get_proxy(); }
  *
  * private:
  *   Glib::Property<int> property_myint_;
@@ -227,6 +228,10 @@ public:
   /** Returns a proxy object that can be used to read or write this property.
    */
   inline Glib::PropertyProxy<T> get_proxy();
+
+  /** Returns a proxy object that can be used to read this property.
+   */
+  inline Glib::PropertyProxy_ReadOnly<T> get_proxy() const;
 };
 
 /** See Property.
@@ -410,6 +415,13 @@ Property<T>::get_proxy()
   return Glib::PropertyProxy<T>(object_, get_name_internal());
 }
 
+template <class T>
+inline Glib::PropertyProxy_ReadOnly<T>
+Property<T>::get_proxy() const
+{
+  return Glib::PropertyProxy_ReadOnly<T>(object_, get_name_internal());
+}
+
 /**** Glib::Property_ReadOnly<T> ****************************************************/
 
 template <class T>