From 004142f85a4c01e11e501ebb440bbf5583710cf3 Mon Sep 17 00:00:00 2001
From: trotFunky <teo.couprie_diaz@telecom-sudparis.eu>
Date: Tue, 14 May 2019 12:43:53 +0200
Subject: [PATCH] Better decltype for Polynomial::add return type

---
 snippets/Polynomial.tpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/snippets/Polynomial.tpp b/snippets/Polynomial.tpp
index 96f06df..04a2dd9 100644
--- a/snippets/Polynomial.tpp
+++ b/snippets/Polynomial.tpp
@@ -35,7 +35,7 @@ public:
     bool equals(const Polynomial<T1>&) const;
 
     template <typename T1>
-    auto add(const Polynomial<T1>& operand) const -> Polynomial<decltype(static_cast<T>(0) + operand[0])>;
+    auto add(const Polynomial<T1>& operand) const -> Polynomial<decltype(T{} + T1{})>;
 
     template <typename T1>
     friend std::ostream& operator<<(std::ostream&, const Polynomial<T1>&);
@@ -62,6 +62,7 @@ private:
 template<typename T>
 Polynomial<T>::Polynomial()
 {
+    // Not bad, but could be better with C++20. Not that useful either
     static_assert(std::is_arithmetic<T>::value,"Polynomial must be of an arithmetic type!");
     factors = {0};
 }
@@ -197,7 +198,7 @@ bool Polynomial<T>::equals(const Polynomial<T1>& operand) const
 
 template<typename T>
 template<typename T1>
-auto Polynomial<T>::add(const Polynomial<T1>& operand) const -> Polynomial<decltype(static_cast<T>(0) + operand[0])>
+auto Polynomial<T>::add(const Polynomial<T1>& operand) const -> Polynomial<decltype(T{} + T1{})>
 {
     bool isLargest = true;
 
@@ -212,7 +213,7 @@ auto Polynomial<T>::add(const Polynomial<T1>& operand) const -> Polynomial<declt
         largestSize = operand.factors.size();
     }
 
-    std::vector<decltype(static_cast<T>(0)+operand[0])> resultPolynomial = {};
+    std::vector<decltype(T{} + T1{})> resultPolynomial = {};
     resultPolynomial.reserve(largestSize);
 
     for(int i = 0;i<smallestSize;i++)
@@ -225,7 +226,7 @@ auto Polynomial<T>::add(const Polynomial<T1>& operand) const -> Polynomial<declt
         resultPolynomial.push_back((isLargest ? factors[i] : operand[i]));
     }
 
-    return Polynomial<decltype(static_cast<T>(0)+operand[0])>(resultPolynomial);
+    return Polynomial<decltype(T{} + T1{})>(resultPolynomial);
 }
 
 ////////////////////