[expected.object.obs] Inconsistency between `value_or()` and `error_or()` in `std::expected<T, E>`

[onihusube]

[expected.object.obs]/21

The return value of value_or() is specified as follows:

Returns: has_value() ? **this : static_cast<T>(std​::​forward<U>(v)).

Meanwhile, the return value of error_or() is specified as follows:

Returns: std​::​forward<G>(e) if has_value() is true, error() otherwise.

Since these functions appear to be dual in nature, it would be preferable to maintain consistent notation. Therefore, should error_or() be modified in this way?

Returns: has_value() ? std​::​forward<G>(e) : error().

There is another problem at this time.

value_or() casts its argument v using static_cast<T>(std::forward<U>(v)). Shouldn't error_or() similarly perform a static_cast<E>?

When the constructor used for conversion is marked as explicit, value_or() will successfully perform the conversion, while error_or() will result in a compilation error.

Here I referred to const & overload, but && overload has the same problem.

[frederick-vs-ja]

LWG issue seems needed. At least, we should be consistent on implicit or explicit conversion for value_or.