Add sampler header file

[ziqizh]

• Add sampler.h under SDK. sampler.h defines sampler and SamplingResult interface.
  Waiting for Support for attributes on spans #117 to merge first.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Oliver Zhang (89ce9f7, e65cf5c, 7b20dc1, 81cb054, b206ced, cdfcd3d, 1f972e0, 5097b2e)

[pyohannes]

This is a good start.

[reyang]

Overall looks good to me, might need to wait for the attributes PR #117.

[ziqizh]

I signed it

[codecov]

Codecov Report

Merging #118 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #118   +/-   ##
=======================================
  Coverage   93.29%   93.29%           
=======================================
  Files          66       66           
  Lines        1656     1656           
=======================================
  Hits         1545     1545           
  Misses        111      111           

[oulin-coder]

Storing a string_view has some pitfalls - string_view is essentially a pointer to an underlying string, so it relies on the underlying string value to outlive the string_view's lifetime. If "key" isn't too large, I recommend just storing it as a string.

[pyohannes]

I have two more nits regarding the doc strings, otherwise this looks good to me. The TODOs for Links and SpanContext can remain, as this is work that still needs to be done and is not part of this PR.

Also, there is no more dependency on #117 any more, so this can be merged as soon as the doc strings are addressed.

Great job!

[pyohannes]

A few more nits. Please make sure you rebase. Then I think this is ready to be merged.

[pyohannes]

Looks all good from my side and ready to merge. @reyang

[reyang]

LGTM, will merge after CI finished.

[ziqizh]

LGTM, will merge after CI finished.

1. Should I change the attributes in SamplingResult from unique_ptr<map> to unique_ptr<const map> since the spec requires attributes to be immutable?
2. I don't have authorization to merge this PR. Do I need to apply for a maintainer role?

[reyang]

1. Should I change the attributes in SamplingResult from unique_ptr<map> to unique_ptr<const map> since the spec requires attributes to be immutable?

This seems to be a nice to have thing. On the other side, I'm guessing even with a const map, the actual value are not guaranteed to be const?

2. I don't have authorization to merge this PR. Do I need to apply for a maintainer role?

Nope.