feat: Memberwise for std::pair<>

[kratsg]

Opening this to make it easier to compare but this is incredibly painful :D See #38 for lengthier details for now.

>>> [i.members for i in eff.member('fBeta_bin_params').tolist()]
[{'first': -1.0, 'second': -2.0}, {'first': 2.0, 'second': 4.0}, {'first': 4.0, 'second': 8.0}, {'first': 8.0, 'second': 16.0}, {'first': 16.0, 'second': 32.0}, {'first': 32.0, 'second': 64.0}, {'first': 64.0, 'second': 128.0}, {'first': 128.0, 'second': 256.0}, {'first': 256.0, 'second': 512.0}, {'first': 512.0, 'second': 1024.0}, {'first': 1024.0, 'second': 2048.0}, {'first': -1.0, 'second': -2.0}, {'first': 1.0, 'second': 1.0}]

[kratsg]

make the ROOT file

$ cat make_tefficiency.py 
import ROOT

fp = ROOT.TFile.Open("test-efficiency.root", "RECREATE")

nbins = 11

h_den = ROOT.TH1F('h_den', 'h_den', nbins, 0, 100)
h_num = ROOT.TH1F('h_num', 'h_num', nbins, 0, 100)

for i in range(1, nbins):
    h_num.SetBinContent(i, 2**i)
    h_den.SetBinContent(i, 2**(i+1))

eff = ROOT.TEfficiency(h_num, h_den)
eff.SetName('TEfficiencyName')
eff.SetTitle('TEfficiencyTitle')

eff.SetBetaBinParameters(0, -1.0, -2.0)
for i in range(1, nbins):
    eff.SetBetaBinParameters(i, 2**i, 2**(i+1))

eff.SetBetaBinParameters(nbins, -1.0, -2.0)

h_den.Write()
h_num.Write()
eff.Write()
fp.Close()

then run it

$ cat debug.py 
import uproot

with uproot.open('test-efficiency.root') as fp:
    eff = fp['TEfficiencyName']

[kratsg]

This portion that we're at right now looks like

--+---+---+---+---+---+---+---+---+---+
  0   0   0 215 190 210   0   0   0  13  
--- --- --- --- --- --- --- --- --- --- 

Unclear what the first 6 bytes are here, but the last 4 seem to be number of elements in the vector (length) in the line below. I assumed it might be 4 bytes / 2 bytes but still not sure what they're meant to match up with.

[kratsg]

here, we make a shell, which means we skip actually reading anything out (in this case, this means "moving the cursor"). We'd just want to inflate all of our classes/objects so we can ask them to each read the file one by one to fill member-wise (see next block).

[jpivarski]

Great! I found a few things to clean up, but I'll be committing them directly to this PR and then merging.

Thanks!

[jpivarski]

I'm going to take this hook out of the if context.get("reading", True) because we're already in the read method. The read_members method, on the other hand, gets entirely skipped.