What does the "-" mean in front of a ruby symbol?

When I had a look into the ActiveRecord source today, I stumbled upon these lines

name = -name.to_s

https://github.com/rails/rails/blob/2459c20afb508c987347f52148210d874a9af4fa/activerecord/lib/active_record/reflection.rb#L24

and

ar.aggregate_reflections = ar.aggregate_reflections.merge(-name.to_s => reflection)

https://github.com/rails/rails/blob/2459c20afb508c987347f52148210d874a9af4fa/activerecord/lib/active_record/reflection.rb#L29

What purpose does the - operator serve for on the symbol name?

>Solution :

That’s String#-@:

Returns a frozen, possibly pre-existing copy of the string.

Example:

a = "foo"
b = "foo"

a.object_id #=> 6980
b.object_id #=> 7000

vs:

a = -"foo"
b = -"foo"

a.object_id #=> 6980
b.object_id #=> 6980