To avoid autovivification of hash elements that might only end up getting used in rvalue context, when you call a function with a hash element as an arg, e.g. foo($hash{$key}), perl invokes a special mechanism.

When perl initially tries to retrieve the hash element before calling the function, if the element doesnt exist, then rather than autovivifying and creating a new null element, it creates a temporary proxy object which has the hash and the key attached to it. When at this point the key is being evaluated, this triggers the first uninit warning. Later inside the function, the value of the proxy object is evaluated during the assignment, which triggers a second (redundant) uninit warning as the undef key is used to retrieve the hash element.

Dave.

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