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C++17 in Detail: A Deep Dive

Evaluation Order in C++17

Explore the changes in evaluation order introduced in C++17 that ensure inner expressions and operator overloads are executed from left to right. Understand how this impacts function chaining and operator overloading behavior, improving code clarity and predictability.

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The example case

C++ 17
#include <iostream>
class Query
{
  public:
    Query& addInt(int i)
    {
      std::cout << "addInt: " << i << '\n';
      return *this;
    }
    Query& addFloat(float f)
    {
      std::cout << "addFloat: " << f << '\n';
      return *this;
    }
};
float computeFloat()
{
  std::cout << "computing float... \n";
  return 10.1f;
}
float computeInt()
{
  std::cout << "computing int... \n";
  return 8;
}
int main()
{
  Query q;
  q.addFloat(computeFloat()).addInt(computeInt());
}

You probably expect that using C++14 computeInt() happens after addFloat. Unfortunately, that might not be the case. For instance here’s an output ...