Detailed Description

template<typename T, typename E>
class gul17::expected< T, E >

An expected<T, E> is an object that normally contains an "expected" object of type T, but it can alternatively contain another, "unexpected" or "error" object of type E.

The main use case of expected is as a function return value. It is a more expressive alternative to the common idiom of returning a bool to indicate success or failure, and using an output parameter to return the result:

std::expected<double, std::string> square_root(double v)
{
    if (v < 0.0)
        return std::unexpected<std::string>("negative value");
    else
        return std::sqrt(v);
}
 
for (double v = -2.0; v <= 2.0; v += 0.5)
{
    auto result = square_root(v);
    if (result)
        std::cout << result.value() << "\n";
    else
        std::cout << result.error() << "\n";
}

Note: The GUL17 version is an adaptation of Sy Brand's implementation (see expected.h) and should behave like std::expected from C++23 for most use cases.

Since: GUL version 2.8.0

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

expected.h