The language has changed in that respect - arrays and hashes only interpolate into double-quoted strings if they end in a postcircumfix, that is any bracketing characters coming after an expression.

say "array: @array";        # interpolates nothing
say "array: @array[]";      # interpolate all elements
say "array: @array[1]";     # interpolate one element
say "array: @array.sort";   # no interpolation, does not
                            # end with something brackety
say "array: @array.sort()"; # interpolates sorted array
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Rakudo implements those cases according to the specification.

See also: strings, arrays, hashes, S02: Literals (scroll down)