my $set = (1, 2, 3).SetHash;
$set.elems == 3 or die "Wrong element count";

# Add a new element.
$set{4} = True;
$set.elems == 4 or die "Wrong element count";

# Add a duplicated element, no effect.
$set{3} = True;
$set.elems == 4 or die "Wrong element count";

# Remove an element.
$set{1} = False;
$set.elems == 3 or die "Wrong element count";

# Remove a non-existing element, no effect.
$set{1} = False;
$set.elems == 3 or die "Wrong element count";