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my @objects = ();
my %unique  = map { "$_" => 1 } @objects;
print sort keys %unique;

Not enough arguments for map at test.pl line 2, near "} @objects"
syntax error at test.pl line 2, near "} @objects"
Execution of test.pl aborted due to compilation errors.

my %unique  = map { ''.$_ => 1 } @objects;