Re: [boost] [outcome] outcome without empty state?

Subject: Re: [boost] [outcome] outcome without empty state?
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-26 15:59:19

> Let me just recall her the suggestion from Peter made in the other thread.
> Mybe have two types:
> `expected<T, E>` does not have the empty state or default constructor -- it
> is used as function's return type
> `prepare_expected<T, E>` is either T or E or Empty -- you use it inside
> function to build expected<T, E>:
> 
>  ```
> expected<T, E> f()
> {
>   prepare_expected<T, E> ans;
>   // populate (or not) ans
>   return ans; // in this conversion you can do all sorts of checks
> }
> ```
> 
> When it comes to converting from `prepare_expected<T, E>` to `expected<T,
> E>`, you have plenty of choices: require manual conversion, narrow-contract
> to be checked, a defensive if and throw... I am just not sure if
> performance can be negatively impacted with this.

I originally considered this design for Outcome's API.

I ended up rejecting it because it's superfluous if you have correctly
designed your expected/outcome/whatever in the first place.

Niall

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