Inside clear_it $data is a local variable that you assign a reference to from the parm stack. the uncommented version then assigns a reference to a empty hash to that local variable. As the subroutine exits the internal $data variable containing the reference is destroyed.
The commented version uses the reference contained in $data as an address to an array and assigns the empty array to that reference

In reply to Re: Pass array, then clear by huck
in thread Pass array, then clear by Anonymous Monk

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