[ ... ] returns a reference to an anonymous array.

{ ... } returns a reference to an anonymous hash.  In the appropriate syntactic context like assignment, that is.  Curlies are used for various things, for example a block, or to group/disambiguate when dereferencing, like @{ $obj->method_that_returns_an_arrayref() }.

In reply to Re^3: Odd number of elements in anon hash by almut
in thread Odd number of elements in anon hash by roibrodo

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