Feature request: addition of etl::expected

[jputcu]

Could it be possible to add etl::expected, matching the c++23 std::expected.
Because the lack of exceptions on my AVR platform, I have used etl::variant for this, but having a more standard way would be better.
This could be a replacement of etl::result.

[jwellbelove]

Thanks, I'll take a look at that

[jwellbelove]

Implementation of etl::unexpected in 20.35.0

[jputcu]

I was planning to use this, but noticed only unexpected was provided.
Looking around I found two nice, active, alternatives:

1. https://github.com/martinmoene/expected-lite
2. https://github.com/TartanLlama/expected

To not reinvent the wheel it would be nice if we could use them, but I quickly run into AVR limitations, e.g. missing utility header. Although etl probably provides everything required.
Could it be possible to provide a layer to satisfy the std library?

This layer would allow more lightweight C++ libraries to be used, e.g. https://github.com/boost-ext/sml.

[jwellbelove]

I have an implementation of etl::expected that's almost complete, but I haven't had time to release it yet.

If you are not using the STL they you could try using a namespace alias...
namespace std = etl;
I haven't tried this myself.
The ETL would also need to have STL style header names for it to work without changing any code.

[jwellbelove]

The trouble with the last thing I said about headers is that the compiler would not be able to distinguish which template library (STL or ETL) to use when it sees something like #include <algorithm>.

[jputcu]

I think all etl headers end with .h, so we could perhaps add a directory with the official headers which forward to the .h headers and alias the namespace?

[jwellbelove]

I think the problem is that if you did that, the compiler will will probably still find its own headers before the ETL's.

#include <algorithm> <<< I think the compiler will choose its own header first.

[jwellbelove]

With GCC it seems you can use -nostdinc++ as a compiler option. I don't know about other compilers.

Edit: There also seems to be a -I option.

[jwellbelove]

Fixed 20.35.12