getInstancesId() would usually mean a singular id corresponding to the group of instances. Only ones with an "s" at the end of the id should return an array if

getInstancesId() would usually mean a singular id corresponding to the group of instances. Only ones with an "s" at the end of the id should return an array if you have the existing "getInstanceId" either that or invert that function to be getIdOfInstance and subsequently getAllIdsOfInstance for the array version. Generally speaking don't use the possessive "s" it is implied by being next to it. Also I usually use "instance" in this case more like an adjective Edit: usually I think of it as (current subject) verb adjective object. So server get instance IDs becomes getInstanceIds() or zoo clean active dogs becomes cleanActiveDogs()