You're confusing functional and OOP-style methods.
Since you define an OOP-style method, you need to invoke it in OOP style.
With your example:
> tmp$`[`("random")
[1] -1.439131143 -0.630354726 0.822006263 -0.651707539 0.475332681
[6] 0.002680224 1.539035675 -0.117609566 2.066227300 1.
I am trying to define subset operator for a reference class and hitting some
problem i am unable to diagnose.To give an example, here is a toy class
generator that is a wrapper around a list
tmpGEN<-setRefClass("TMP", fields=list(
namelist="list"
