I smiled when I came upon the '_ref' suggestion, recognizing it as a practice I already followed, sort of. Like you, I don't need the 'ef' part of that tag chewing up valuable line space and/or adding clutter. However, rather than just stopping at '_r', I DO like inserting an extra character to indicate the kind of reference I expect to be referencing. As in:

    _ar for array ref
    _hr for hash ref
    _xr for code ref
    _sr for scalar ref
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The program I'm writing has grown to be many lines and I prefer as much clarity as possible when I reread sections of it. If helps document my intentions which helps when refactoring. And with all the subroutines I end up inventing, it makes for a clear set of expectations of what variables should be passed to the subroutine without having to use prototypes.

    sub foo {
        my (
            $camels_ar,
            $votes_hr,
            $count_mechanism_xr,
        ) = @_;
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Frankly, I wish more books that teach Perl would use this approach because as the learner, it's hard enough trying to understand some new idea without having to fight through the additional ambiguity of "now what's in this variable and why is it written up that way?"