irb(main):002:0> a = 1; b = 2; x = true # Ruby 1.9.3

irb(main):022:0* if x then  a, b = b, a else  a, b = a + 1, b + 1 end
=> [2, 1]
irb(main):023:0> x ? a, b = b, a : a, b = a + 1, b + 1
SyntaxError: (irb):23: syntax error, unexpected ',', expecting ':'
x ? a, b = b, a : a, b = a + 1, b + 1
      ^
(irb):23: syntax error, unexpected ':', expecting $end
x ? a, b = b, a : a, b = a + 1, b + 1
                 ^

Have I to use the extended if form for such type of assignment, or is
there a way to rewrite the ? : form?