It's because of the ampersands, see perlsub:
Not only does the & form make the argument list optional, it also disables any prototype checking on arguments you do provide. 
$ perl -le 'sub foo(\@) { ref(shift) ? "ref" : "not a ref" }; @arr=(1.
+.3); print foo(@arr)'
ref

$ perl -le 'sub foo(\@) { ref(shift) ? "ref" : "not a ref" }; @arr=(1.
+.3); print &foo(@arr)'
not a ref

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In reply to Re: Dereferencing arrays by hazylife
in thread <SOLVED>Dereferencing arrays by divitto

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