etl::optional cannot return an optional object of self from member function

[jovere]

In the etl::optional code, it is required that the type be is_pod, aka. "plain old data". Why is this? Why can't I have an optional of a more complex data type?

For reference: https://github.com/ETLCPP/etl/blob/0f1840a70d11a3d317afa55b8361829b93c8eeb8/include/etl/optional.h#L107

[jwellbelove]

ETL's optional can used with both POD and complex types. There are two specialisations:- One where the type is a POD. etl::optional<T, true> The other where the type is not POD. etl::optional<T, false>

The true or false is automatically determined by the declaration template <typename T, bool is_pod = etl::is_pod<T>::value>

[jwellbelove]

etl::optional<int> instantiates etl::optional<int, true> etl::optional<std::string> instantiates etl::optional<std::string, false>

[jovere]

My apologies, It appears that I was incorrect in the reading of the error. I plugged it into godbolt (https://godbolt.org/z/PE91sxhaz) and figured out the actual error.

It won't let me return an optional value of the class itself from a member function, since it is forward declared. This is an issue, since we have a static member function to create an object from a string. I've also shown that it works fine with the standard library version. I have also tried boost and it works as expected. The code on godbolt (https://godbolt.org/z/PE91sxhaz) is shown below for posterity:

#include <string>
#include <optional>
#include "etl/optional.h"

class etl_optional_dataType{    

public:
    static etl::optional<etl_optional_dataType> createItemFromString(std::string data) // Won't compile
    {
        return {};
    }
};

class std_optional_dataType{
public:
    static std::optional<std_optional_dataType> createItemFromString(std::string data) // Compiles
    {
        return {};
    }
};

[jwellbelove]

Looks like I may have to do the POD optimisations differently.

[jwellbelove]

Fixed 20.38.11