>   b += "thing" # b = b + "thing"
> 
>  the variable `b', now, make reference to this new object

Olivier,

You can use << instead of += to do what you want:

irb(main):010:0> a="thingy"
"thingy"
irb(main):011:0> b=a
"thingy"
irb(main):012:0> b << "thing"
"thingything"
irb(main):013:0> a
"thingything"

Chris