The call works because the prototype forces the arguments to be references. From the Prototypes section in perlsub:

Any backslashed prototype character represents an actual argument that absolutely must start with that character. The value passed as part of @_ will be a reference to the actual argument given in the subroutine call, obtained by applying \ to that argument.

However, in general it is best to avoid prototypes exactly because they cause this sort of confusion.

DWIM is Perl's answer to Gödel

In reply to Re^2: Subroutine Parameters by GrandFather
in thread Subroutine Parameters by radicalfix

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