One problem:

$x = shift || 4;
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What happens if you really want to pass 0 in? It just won't work. So you still end up with a defined test (or apply the "defined or" patch):

$x = shift;
$x = defined $x ? $x : 4;

# Or with the "defined or" patch
$x = shift // 4;

# Or check if there is anything left on @_ and shift if there is
$x = @_ ? shift : 4;
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