Update: hmm... on further reading, I think the original point was that you don't need the scalar instead of the notion that adding parens would clarify what keys was doing.... so, nevermind.

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Why would the parens make it any clearer? I think you might be misunderstanding whats happening here. From keys:

In a scalar context [keys], returns the number of keys [in the hash]

Comparing this to length (since it behaves in a similiar way) which of these is clearer:

$x = length $y;
$x = (length $y);
[download]

It looks like you think (keys %y) behaves like @{[keys %y]}... i.e. return the list of keys, package them up into an array, then return the member count of the array.

-Blake