Modern C++ idoms and recipes

meshell
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std::optional

C++17 adds template std::optional to manage an optional value.

DIY

Try to make pass the tests for error cases. Do not worry about the good case test, if it fails because of formating or precision issues.

Make the tests pass by refactoring function differentiate to return std::optional<double> instead of double. Does it help to make use of value_or()?

Refactor the code to use std::optional
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#include <functional>
#include <sstream>
#include <string>
// symmetric difference quotient
double differentiate(std::function<double(double)> f, double h, double x)
{
return (f(x + h) - f(x - h)) / (2 * h);
}
std::string estimated_velocity(std::function<double(double)> distance, double time, double precision)
{
auto velocity = differentiate(distance, precision, time);
std::stringstream output;
output << "Estimated velocity after " << time << " seconds is " << velocity << " m/s.";
return output.str();
}
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Bonus exercise

Replace the type for time with something better than than double.

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