From ab71ecdf3867a3f788be7c75f3842e792e3d76da Mon Sep 17 00:00:00 2001
From: Parth <partharora99160808@gmail.com>
Date: Thu, 8 Apr 2021 21:36:46 +0530
Subject: [PATCH] Refactor TFormula::Eval() to reduce code duplication

---
 hist/hist/inc/TFormula.h   | 21 +++++++++++++++++----
 hist/hist/src/TFormula.cxx | 36 ------------------------------------
 2 files changed, 17 insertions(+), 40 deletions(-)

diff --git a/hist/hist/inc/TFormula.h b/hist/hist/inc/TFormula.h
index 6ad9f7b670093..28663f9879281 100644
--- a/hist/hist/inc/TFormula.h
+++ b/hist/hist/inc/TFormula.h
@@ -199,10 +199,8 @@ class TFormula : public TNamed
    Int_t          Compile(const char *expression="");
    void   Copy(TObject &f1) const override;
    void   Clear(Option_t * option="") override;
-   Double_t       Eval(Double_t x) const;
-   Double_t       Eval(Double_t x, Double_t y) const;
-   Double_t       Eval(Double_t x, Double_t y , Double_t z) const;
-   Double_t       Eval(Double_t x, Double_t y , Double_t z , Double_t t ) const;
+   template <typename... Args>
+   Double_t       Eval(Args... args) const;
    Double_t       EvalPar(const Double_t *x, const Double_t *params = nullptr) const;
 
    /// Generate gradient computation routine with respect to the parameters.
@@ -314,4 +312,19 @@ void TFormula::SetParNames(Args &&...args)
       if(!name.empty()) SetParName(i++, name.c_str());
    }
 }
+
+////////////////////////////////////////////////////////////////////////////////
+/// Set first 1, 2, 3 or 4 variables (e.g. x, y, z and t)
+/// and evaluate formula.
+
+template <typename... Args>
+Double_t TFormula::Eval(Args... args) const 
+{
+   if (sizeof...(args) > 4) {
+      Error("Eval", "Eval() only support setting upto 4 variables");
+   }
+   double xxx[] = {static_cast<Double_t>(args)...};
+   return EvalPar(xxx, nullptr);
+};
+
 #endif
diff --git a/hist/hist/src/TFormula.cxx b/hist/hist/src/TFormula.cxx
index a5f4f0c0b0daf..1add76d5e6240 100644
--- a/hist/hist/src/TFormula.cxx
+++ b/hist/hist/src/TFormula.cxx
@@ -3360,42 +3360,6 @@ ROOT::Double_v TFormula::EvalParVec(const ROOT::Double_v *x, const Double_t *par
 }
 #endif
 
-////////////////////////////////////////////////////////////////////////////////
-/// Sets first 4  variables (e.g. x, y, z, t) and evaluate formula.
-
-Double_t TFormula::Eval(Double_t x, Double_t y, Double_t z, Double_t t) const
-{
-   double xxx[4] = {x,y,z,t};
-   return EvalPar(xxx, nullptr); // takes care of case where formula is vectorized
-}
-
-////////////////////////////////////////////////////////////////////////////////
-/// Sets first 3  variables (e.g. x, y, z) and evaluate formula.
-
-Double_t TFormula::Eval(Double_t x, Double_t y , Double_t z) const
-{
-   double xxx[3] = {x,y,z};
-   return EvalPar(xxx, nullptr);
-}
-
-////////////////////////////////////////////////////////////////////////////////
-/// Sets first 2  variables (e.g. x and y) and evaluate formula.
-
-Double_t TFormula::Eval(Double_t x, Double_t y) const
-{
-   double xxx[2] = {x,y};
-   return EvalPar(xxx, nullptr);
-}
-
-////////////////////////////////////////////////////////////////////////////////
-/// Sets first variable (e.g. x) and evaluate formula.
-
-Double_t TFormula::Eval(Double_t x) const
-{
-   double * xxx = &x;
-   return EvalPar(xxx, nullptr);
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 /// Evaluate formula.
 /// If formula is not ready to execute(missing parameters/variables),