So do I, but $n = scalar foo does something completely different from $n = () = foo.

Observe, I have nothing up my sleeve!

sub foo { 5, 17 }       # sub returning 2 values
my $n1 = () = foo;      # $n1 == 2
my $n2 = scalar foo;    # $n2 == 17
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You forgot the general rule about converting a list to a scalar: "there is no general rule for converting a list to a scalar"!