[] operator

/datum/tester
    var/obj/O = new /obj{name = "TEST OBJ"}
    var/mob/M = new /mob{name = "TEST mob"}

/datum/tester/operator[](idx)
    world.log << "got index: [idx]"
    if(idx == "obj") return O
    return M

/datum/tester/proc/tellme()
    world.log << "I am called"

/proc/main()
    var/datum/tester/D = new()
    D["obj"]