The Bit Bang You Are Completed package is Yet Another Completion
method.

Say you have a Lisp variable named
this-is-a-very-long-variable-for-example, in the buffer in which
this name is already typed, you can type tvvf and then press M-g
<return> to complete it.  You can type tvx or even tx for the same
effect, if you like.

There are also other completing methods, for e.g., to complete
arbitrary strings, whole lines, sexp and paragraphs. The last two
is not as useful as the others.

For more information see the readme at:
https://github.com/baohaojun/bbyac