[Rivet-svn] rivet: Fix tricky object lifetime bug affecting WFinder users

[Rivet Mercurial]

details:   https://rivet.hepforge.org/hg/rivet/rev/1c2c3599115e
branches:  release-2-6-x
changeset: 6342:1c2c3599115e
user:      David Grellscheid <david.grellscheid at durham.ac.uk>
date:      Fri Jun 22 18:51:03 2018 +0100
description:
Fix tricky object lifetime bug affecting WFinder users

So far, taking a const reference to WFinder::constituentLepton() or
...Neutrino() was unsafe, since they internally rely on returning
a temporary value from the filter_select() tools which goes out of scope
immediately.

Projections need to store such temporaries themselves in member variables.

diffs (truncated from 79 to 50 lines):

--- a/include/Rivet/Projections/WFinder.hh	Thu Jun 21 22:59:23 2018 +0100
+++ b/include/Rivet/Projections/WFinder.hh	Fri Jun 22 18:51:03 2018 +0100
@@ -101,20 +101,20 @@
 
     /// @brief Access to the Ws' constituent clustered leptons
     /// @note Either size 0 if no boson was found or 1 if one boson was found
-    const Particles constituentLeptons() const;
+    const Particles& constituentLeptons() const { return _leptons; }
     /// brief Access to the W's constituent clustered lepton (assuming it exists)
     /// @todo C++17 std::optional...
-    const Particle constituentLepton() const { return constituentLeptons().front(); }
+    const Particle& constituentLepton() const { return _leptons.front(); }
 
 
     /// Access to the Ws' constituent neutrinos
     ///
     /// @note Either size 0 if no boson was found or 1 if one boson was found
     /// @note The neutrino can't be perfecly reconstructed -- this is a pseudo-nu from the MET.
-    const Particles constituentNeutrinos() const;
+    const Particles& constituentNeutrinos() const { return _neutrinos; }
     /// Access to the W's constituent neutrino (assuming it exists)
     /// @note The neutrino can't be perfecly reconstructed -- this is a pseudo-nu from the MET.
-    const Particle constituentNeutrino() const { return constituentNeutrinos().front(); }
+    const Particle& constituentNeutrino() const { return _neutrinos.front(); }
 
 
     /// Access to the particles other than the W leptons and clustered photons
@@ -167,6 +167,9 @@
     /// Charged lepton flavour
     PdgId _pid;
 
+    /// Result caches. Will be filled by project()
+    Particles _leptons, _neutrinos;
+
   };
 
 
--- a/src/Projections/WFinder.cc	Thu Jun 21 22:59:23 2018 +0100
+++ b/src/Projections/WFinder.cc	Fri Jun 22 18:51:03 2018 +0100
@@ -72,18 +72,6 @@
 
 
 
-  const Particles WFinder::constituentLeptons() const {
-    if (empty()) return Particles();
-    return boson().constituents(isChargedLepton);
-  }
-
-
-  const Particles WFinder::constituentNeutrinos() const {