Keeping track of number of entries with weighted storage

[alexander-held]

Can boost-histogram keep track of the number of entries when using a weighted storage? I believe at the moment uproot does not save such information, but I am not sure if this is currently tracked and if it could be saved correctly or is just not present at all.

import ROOT
import boost_histogram as bh
import uproot

h = ROOT.TH1D('h', 'h', 10, 0, 1)
h.Fill(0.2, 0.1)
h.Fill(0.4, 0.5)
assert h.GetEntries() == 2.0  # 2 entries in the histogram

# create the same histogram with boost-histogram
h = bh.Histogram(bh.axis.Regular(10, 0, 1), storage=bh.storage.Weight())
h.fill([0.2, 0.4], weight=[0.1, 0.5])

# save with uproot, load with ROOT
with uproot.recreate("tmp.root") as f:
    f["h"] = h

f = ROOT.TFile.Open("tmp.root")
f["h"].GetEntries()  # this is 0.6 now, but should probably be 2?