gtk:entry-completion-compute-prefix (completion key)

completion -- a gtk:entry-completion object
key -- a string for the text to complete for

The string for the common prefix all rows starting with key or nil if no row matches key.

Computes the common prefix that is shared by all rows in completion that start with key. If no row matches key, the nil values will be returned. Note that a text column must have been set for this function to work, see the gtk:entry-completion-text-column function for details. The gtk:entry-completion implementation is deprecated since 4.10. This object will be removed in GTK 5.