Make_gen_with_creators.TThe iter argument to Container.Make specifies how to implement the container's iter function. `Define_using_fold means to define iter via:
iter t ~f = Container.iter ~fold t ~f`Custom overrides the default implementation, presumably with something more efficient. Several other functions returned by Container.Make are defined in terms of iter, so passing in a more efficient iter will improve their efficiency as well.
val length : [ `Define_using_fold | `Custom of ('a, 'phantom) t -> int ]The length argument to Container.Make specifies how to implement the container's length function. `Define_using_fold means to define length via:
length t ~f = Container.length ~fold t ~f`Custom overrides the default implementation, presumably with something more efficient. Several other functions returned by Container.Make are defined in terms of length, so passing in a more efficient length will improve their efficiency as well.
val concat_of_array : 'a array -> ('a, _) concat