std::expected -- what can you do with it?
There's a fancy new thing in C++: std::expected. There's a lot of pots about it's awesomeness, but what is it, really?
Answer: if you've got a std::expected, you can do three important things. Let's give a name to our std::expected: it's called result. And as a reminder: std::expected holds one of two values, which in this post I'll cleverly call "first" or "second".
1. Just result by itself is a bool. When first is set, it returns true; when second is set, false.
2. *result is just first.
3. result.error() returns second.
You can also chain them together, assuming you have code where you want to do a bunch of stuff in order and will never have to refactor the code to be multi-threaded, or handle error conditions weirdly, or log something and then fail, or a lot of things. Oh, and using functions means lots of global variables, and the function must return a std::expected, not an int.
1. result.and_then(function) will call function with *result. The function can take exactly one variable, and the function will only be called if result was set to first.
2. result.or_else(function) is like the opposite of and_then. It's also a function that takes a single parameter (love them globals!) but take in the type of second, not first, and is only called if the second was set (the 'unexpected' branch).
Want to make a std::expected?
And some useless crap
What if you you've got a std::expected where first is an int, but you really need a double? Can you cast it? Nope, you can't. Casting is now called "transform".
There's a tranform_error(), too.
First thoughts: what about exceptions?
Lord knows. I guess exceptions aren't a thing any more?
What happens if I need to set a breakpoint? Answer: good luck with that.
The source code the std::expected iat about 1500 lines of
