In perlsecret - perl secret operators, there's 
# remove empty array refs
@arrays = ( [], [1], [ 1, 2 ], [], [ 5 .. 9 ] );

# @filled = ( [1], [ 1, 2 ], [ 5 .. 9 ] );
@filled = grep +()= @$_, @arrays;

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with a note of:
(The + is in the above line is a no-op, used to tell grep that the parentheses are not enclosing its arguments.)
what does that note actually mean?

In reply to Perlsecret - plus no-ops by Anonymous Monk

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