Re: [boost] [outcome] How to drop the formal empty state

Subject: Re: [boost] [outcome] How to drop the formal empty state
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-25 15:14:33

>> I'd therefore be happier with default construction giving
>> uninitialised contents, or a default constructed T or E. No
>> overloading state of E.
> 
> result and outcome have no E. I'm not talking about E or expected<T, E>
> here. I'm talking specifically about result<T> and outcome<T>. That is,
> I'm trying to answer the question "Under the assumption that expected<T,
> E> doesn't exist, what should the default constructor of result<T> do?"
> 
> Default constructing to an std::error_code of 0 is kind of stupid
> because "The operation failed: The operation succeeded", although one
> might, I suppose, make an argument in favor of constructing into a
> stupid state precisely because it's stupid.

I'd choose uninitialised bytes or default constructing T before default
constructing E to a null error_code. As I've mentioned many times now,
default constructed error_code is only by convention not an error, the
unfortunate choice of the system_category by the C++ standard makes it
not portable to assume a default constructed error_code is not an error.

If people did agree with me that a default trapping empty state is
particularly useful in debug builds, the obvious choice for a release
build default is uninitialised bytes. As Vicente mentioned, valgrind and
the AddressSanitizer should catch misuse of those.

Niall

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