>
> we should be able to not require them to be set and assume the defaults?
What happens when we add a field without a default value to the message?
If users can assume they don't need to set the message this may cause
backwards compatibility issues in the future.
Maybe I am not understanding whether you mean leaving the message unset, or
the field?
—
*Joris Van Remoortere*
Mesosphere
On Thu, Feb 2, 2017 at 3:06 PM, Yan Xu <xuj...@apple.com> wrote:
> With protobuf you can specify custom default values for scalar types
> (proto2 at least) but not message types, e.g.,
>
> ```
> message Filters {
> // Time to consider unused resources refused. Note that all unused
> // resources will be considered refused and use the default value
> // (below) regardless of whether Filters was passed to
> // SchedulerDriver::launchTasks. You MUST pass Filters with this
> // field set to change this behavior (i.e., get another offer which
> // includes unused resources sooner or later than the default).
> optional double refuse_seconds = 1 [default = 5.0];
> }
> ```
>
> However, the message `Filters` essential has a default value because *all*
> its
> fields have default values. It all depends on whether the receiver chooses
> to check it is not set or directly accesses it and gets the default values.
>
> When we reference the type in other messages, e.g.,
>
> ```
> message Accept {
> repeated OfferID offer_ids = 1;
> repeated Offer.Operation operations = 2;
> optional Filters filters = 3;
> }
> ```
>
> We are not explicitly telling users what's going to happen when `filters`
> is not set. The master just directly uses it without checking.
>
> It does feel intuitive to me that "*if all the fields in a message have
> default values, and it semantically feels like a config, then we can just
> interpret them when unset as indication to use defaults*".
>
> However we probably should document it better.
>
> To generalize it further, for something like this with multiple fields
>
> ```
> message ExponentialBackoff {
> optional double initial_interval_seconds = 1 [default = 0.5];
> optional double max_interval_seconds = 2 [default = 300.0];
> optional double randomization_factor = 3 [default = 0.5];
> optional double max_elapsed_seconds = 4 [default = 2592000.0];
> }
> ```
>
> we should be able to not require them to be set and assume the defaults?
>
> One step further, if the message has recursively nested messages with
> default values, we can treat the parent message as having a default value
> too?
>
> Thoughts?
>
> Yan
>
