From type/Baggy

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method SetHash(--> SetHash:D)

Returns a SetHash whose elements are the keys of the invocant.

my $breakfast = (eggs => 2, bacon => 3).BagHash;
my $sh = $breakfast.SetHash;
say $sh.^name;                            # OUTPUT: «SetHash␤» 
say $sh.elems;                            # OUTPUT: «2␤»

From type/Any

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method SetHash(--> SetHash:D) is nodal

Coerces the invocant to SetHash, whereby Positional are treated as lists of values.