Holds either a value of type T or an error of type E, like a minimal version of C++23's std::expected. More...

#include <Expected.hpp>

Public Member Functions
constexpr	Expected (T value)
constexpr	Expected (Unexpected< E > unexpected)
constexpr bool	has_value () const
constexpr	operator bool () const
constexpr const E &	error () const
	The error. It is an error to call this if has_value() is true.

constexpr const T &	value () const &
	The value. It is an error to call this if has_value() is false.
constexpr T &	value () &
	The value. It is an error to call this if has_value() is false.
constexpr T &&	value () &&
	The value. It is an error to call this if has_value() is false.

Detailed Description

template<typename T, typename E>
class Expected< T, E >

Holds either a value of type T or an error of type E, like a minimal version of C++23's std::expected.

Construct an Expected from a T to hold a value, or from an Unexpected<E> to hold an error. Return an Expected from functions that can fail to let the caller decide how to handle the failure.

Expected<double, SqrtError> checked_sqrt(const double x) {
  if (x < 0.0) {
    return Unexpected{SqrtError::Negative};
  }
  if (x == std::numeric_limits<double>::infinity()) {
    return Unexpected{SqrtError::Infinite};
  }
  return sqrt(x);
}
 
double sqrt_or_zero(const double x) {
  const auto result = checked_sqrt(x);
  if (not result.has_value()) {
    return result.error() == SqrtError::Negative ? 0.0 : x;
  }
  return result.value();
}

Calling value() when there is an error, or error() when there is a value, is an error (also in release builds).

Unlike std::expected, this class stores both a T and an E, so both must be default-constructible and the one that isn't held is default-constructed. This keeps the class simple.

The documentation for this class was generated from the following file:

src/Utilities/Expected.hpp

Public Member Functions

Detailed Description