+= is not equivalent to =+. This shows some about how.

equals_plus_does_not_equal_plus_equals.txt

2.0.0-p247 :005 > pp Ripper.lex('foo += 1');nil
[[[1, 0], :on_ident, "foo"],
 [[1, 3], :on_sp, " "],
 [[1, 4], :on_op, "+="],
 [[1, 6], :on_sp, " "],
 [[1, 7], :on_int, "1"]]
 => nil
2.0.0-p247 :006 > pp Ripper.lex('foo =+ 1');nil
[[[1, 0], :on_ident, "foo"],
 [[1, 3], :on_sp, " "],
 [[1, 4], :on_op, "="],
 [[1, 5], :on_op, "+"], <== this is the unary + operator, which does nothing.
 [[1, 6], :on_sp, " "],
 [[1, 7], :on_int, "1"]]
 => nil