Gtk.TreeSortable.prototype.set_sort_func

function set_sort_func(sort_column_id:Number, sort_func:Gtk.TreeIterCompareFunc):void {
    // Gjs wrapper for gtk_tree_sortable_set_sort_func()
}

Sets the comparison function used when sorting to be sort_func. If the current sort column id of sortable is the same as sort_column_id, then the model will sort using this function.