Re: [boost] [outcome] Ternary logic -- need an example

Subject: Re: [boost] [outcome] Ternary logic -- need an example
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-19 22:03:43

>>> A program might return an outcome containing a null
>>> error_code. It probably is a bug,
>>
>> Interesting. I need to think about it. But my first response would be. If
>> a user cheats the system in this way, you should not try to rescue the
>> situation.
> 
> I can think of two ways of looking at the situation with a
> value-initialized error code:
> 
> 1. Class outocme<T> has an invariant: putting it into state where it stores
> a value-initialized error code is a bug, close to undefined behavior, which
> means, you can assert() inside and users and algorithms  can expect it
> never happens.

I am afraid I don't understand. A value initialised error code is surely
a normal error code? Why would I need to assert stuff?

> 2. Class outcome<T> can be in yet another state: "strange". So we have the
> following states: valued, exceptional, errored, empty, and strange. And the
> user when inspecting the state has to take into account all the five
> possible states.

Every additional possible state generates more branches for the
compiler's optimiser to deal with. I would therefore reject any
additional possible states.

Niall

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