Add a Traits type about analytics-go

[f2prateek]

I don't believe that traits are standardized like context. https://cloudup.com/c3KQOQu-Owa

Like properties, some fields are standardized, but it is definitely acceptable for customers to be able to set their own keys for traits.

[achille-roussel]

The documentation says The following is all the reserved traits we’ve standardized:, how about taking the same approach that we have with the Context type, defining the structure with all fields from the specs and adding an Extra map for extensions?

[f2prateek]

Traits are certainly meant to be a free form dictionary and this is a very common use case - so I wouldn't like to hide custom ones behind the Extras. I think it degrades the API (didn't matter much in the context because there is a very limited number of cases when you'd use something beyond what we've sped'd).

analytics.Traits{
  Age: 21,
  Extras: map[string]interface{}{
    "plan": "developer",
  },
}

vs.

map[string]interface{}{
  "age": 21,
  "plan": "developer",
}

[achille-roussel]

OK.

Yeah as I'm reading more in details, pretty much everything is a string except dates but it says the API is flexible and accepts different formats... It doesn't look like there's much needs to do sanity checks client side.

Thanks for the insights!

[f2prateek]

FWIW, I like what we've done in the Android library the best - we let users use a map and the traits type independently. This gives users the option to use the regular Java Map API:

new HashMap<>().put("age", 21).put("plan", developer")

Or use the specific implementation of our Map type (traits) which adds type safe setters for the spec'd fields.

new Traits().putAge(21).put("plan", developer")

And then this works great things like properties as well:

new Properties().putRevenue(21.09).putCurrency("usd").put("custom", "custom");

[achille-roussel]

Hm interesting, I'm gonna think about it a little bit and see if we can figure something that works well in Go.