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Subject: Re: [boost] [outcome] Change semantics on UB from peer review agreed semantics?
From: Gavin Lambert (boost_at_[hidden])
Date: 2018-09-13 00:11:54

Mere moments ago, quoth I:
> Perhaps boost::throw_error, which is expected to internally construct an
> appropriate exception based on its argument type and then call
> boost::throw_exception?

To clarify, I was wondering if we should:

  1. Implement an error-to-exception conversion trait as a generic
template which does not compile by default.
  2. Provide a specialisation for boost::system::error_code which
returns boost::system::system_error.
  3. (Where supported by the STL) Provide a specialisation for
std::error_code which returns std::system_error.
  4. Allow users to provide additional specialisations for other error
  5. Provide generic boost::throw_error which calls
boost::throw_exception on the result of the conversion trait.
  6. Make Outcome's default policy call boost::throw_error instead of
hard UB.

The people who want hard UB can still use a policy that requests it.

Everyone else will get a compile error until they either implement the
conversion trait, use an error_type which is already implemented, or
switch to a UB policy.

Bonus: the conversion trait provides an easy way to ask metaprogramming
questions such as "what is the exception type for this error code" or
"is this a throwable error code type".

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