GTK EntryCompletion by insertion instead of replacement - autocomplete

Question

I've built a GTK application with autocompletion in an Entry, but I'd like the selected "completion" string to be replace the only word that the cursor touches, whereas it currently replaces all text in the Entry.
I can use set_match_func on the EntryCompletion to deliver matches based on only the word that is adjacent to the cursor, but I don't see how to override the text-insertion behaviour. Is there a way for me to do this?
I'm working in Ruby with gtk3. (I linked the doc for gtk2 because for the life of me, I can't find a complete doc for gtk3 in Ruby.)
Edit Here's my implementation (in Ruby), which lacks the desired "insert" behaviour:
module MyAutocomplete
# Add autocomplete to a Gtk::Entry object
def self.add entry, &block
model = Gtk::ListStore.new String
model.append.set_value 0, 'sd'
model.append.set_value 0, 'foo'
model.append.set_value 0, 'six'
completion = Gtk::EntryCompletion.new
completion.set_minimum_key_length 0
completion.set_text_column 0
completion.set_inline_completion true
completion.set_model model
completion.set_match_func do |*args|
self.match_func *args
end
yield(model, completion) if block_given?
entry.set_completion completion
end
def self.match_func(entry_completion, entry_value, list_obj)
len = 0 # Counts characters into the entry text
cursor = entry_completion.entry.position
entry_text = entry_completion.entry.text
entry_tokens = entry_text.scan(/[\w+#]+|[^\w#]+/)
current_token = entry_tokens.find { |tok|
(len += tok.length) >= cursor && tok =~ /\w/
}
obj_text = list_obj.get_value(0)
return current_token && obj_text.start_with?(current_token)
end
end