MetricVec was already exported in early versions of this library, but
nobody really used it to implement vectors of custom Metric
implementations. Now #796 has shown up with a fairly special use case
for which I'd prefer a custom implementation of a special
"auto-sampling histogram" outside of this library. Therefore, I'd like
to reinstate support for creating vectors of custom Metric
implementations.
I played around for quite some while with the option of a separate
package providing the tools one would need to create vectors of custom
Metric implementations. However, with the current structure of the
prometheus/client_golang/prometheus package, this leads to a lot of
complications with circular dependencies. (The new package would need
the primitives from the prometheus package, while the existing metric
vectors like GaugeVec need to import the new vector package to not
duplicate the implementation. Separating vector types from the main
prometheus package is out of the question at this point because that
would be a breaking change.)
Signed-off-by: beorn7 <beorn@grafana.com>
beorn7