PSA: Replacing RTCStatsMember<T> with absl::optional<T> in progress, use Attributes() instead of Members()

[Henrik Boström]

Hello,

In an effort to reduce the number of special purpose constructs in favor of more standard ones, RTCStatsMember<T> and its abstraction RTCStatsMemberInterface will be removed in favor of using absl::optional<T> to represent GetStats() statistics.

For those referring the C++ fields of the RTCStats objects directly, little will change but you should make sure to use `stat.has_value()` instead of `stat.is_defined()` to be compatible with the upcoming absl::optional<T> change.

For those iterating all stats members in a more abstract way, you need to migrate from RTCStats::Members() returning a list of const RTCStatsMemberInterface* to RTCStats::Attributes(), returning a list of Attributes. The Members() method will soon be deleted.

The Attribute can be used in a similar way as RTCStatsMemberInterface, e.g.

```

// for each attribute in rtc_stats.Attributes()...

if (!attribute.has_value())

  continue;

if (attribute.holds_alternative<std::string>()) {

  RTC_LOG(LS_INFO) << attribute.name() << " is a string with value: \"" << attribute.get<std::string>() << "\".";

}

```

For reference, here is an example of migrating from members to attributes.

[Kostya Vasilyev]

Hello,

If the motivation is to use standard constructs, maybe consider std::optional instead of absl::optional?

— K

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[Philipp Hancke]

absl::optional is an alias for std::optional (for Chromium, 

  https://groups.google.com/a/chromium.org/g/chromium-dev/c/nV0PlRJTg-U/m/7alTn9RfAAAJ

but moving forward it might indeed make sense to just write it as such.

Given almost 5000 use of absl::optional I doubt anyone wants to do a search-replace, maybe after next Christmas ;-)

To view this discussion on the web visit https://groups.google.com/d/msgid/discuss-webrtc/9425FF2F-FC35-459D-BC0B-BC31614BBD42%40justin.tv.

[Henrik Boström]

For now, all of webrtc uses absl::optional rather than std::optional so we should be consistent. But I think you're right in that we can change from absl to std, I asked around and AFAIK there is nothing blocking that. But that's a separate effort.