$ curl cheat.sh/
# complete
# Provides argument autocompletion to shell commands.
# More information: <https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion-Builtins.html>.

# Apply a function that performs autocompletion to a command:
complete -F function command

# Apply a command that performs autocompletion to another command:
complete -C autocomplete_command command

# Apply autocompletion without appending a space to the completed word:
complete -o nospace -F function command

$
Follow @igor_chubin cheat.sh tldr