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Subject: [boost] [outcome] v2.1 progress report
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2018-04-03 20:02:09

Dear Boost,

Two months after you accepted Outcome into Boost, I am pleased to say
that I believe that all the known bugs and very substantial source
refactoring recommended by the peer review have been implemented
(detailed changelog is appended below). What remains is a few months of
maturing in real world use as all this severe refactoring needs to be
tested outside a test suite, and of course the documentation which I
don't intend to start work on until the autumn.

The Boost edition has, obviously, received a major upgrade and it is now
100% "Boost native" in that it uses Boost.System and Boost.Exception
now. The test suite for the Boost edition exclusively tests the Boost
native edition, and it all passes. Outcome (both standalone and Boost
editions) now can handle both Boost and std types freely intermixed as
you see fit.

A new "lite" single header edition exists which drags in virtually no
system headers, and is hideously low impact on compile times as a
result. ABI and API stability have been dumped to git repo with
scripting to check the current library against the frozen dumps. This
edition should make the corporate crowd very pleased.

Very little should appear to have changed from the outside. Code written
for v2.0 ought to, more or less, compile and work as before with v2.1.

I would appreciate whatever help the Boost community can give in helping
to test this edition. I expect new bugs to have been introduced given
the severe source code refactoring, and new dual support for Boost and
std as equals.

My gratitude in advance.


## v2.1 in progress [[project]](
- Boost edition is now 100% Boost, so defaults for `result` and
`outcome` are `boost::system::error_code::errc_t` and
`boost::exception_ptr`. Moreover, the test suite in the Boost edition
now exclusively tests the Boost edition. One can, of course, freely use
the standalone edition with Boost, and the Boost edition with `std` types.
- Renamed ADL discovered customisation point
to `outcome_throw_as_system_error_with_payload()`.
- [#135](
    - Added much clearer compile failure when user tries `result<T, T>`
or `outcome` where two or more types are identical. Thanks to Andrzej
Krzemieński for suggesting a technique which combines SFINAE correctness
with the remaining ability for `result<T, T>` etc to be a valid type,
but not constructible.
- [#67](
    - Fixed one of the oldest long open bugs in Outcome, that the
noexcept unit tests failed on OS X for an unknown reason.
- [#115](
    - Outcome did not construct correctly from `failure_type`.
- Inexplicably outcome's error + exception constructor had been removed.
Nobody noticed during the Boost peer review, which is worrying seeing as
that constructor is needed for one of the main advertised features to Boost!
- [#107]( and
    - `operator==` and `operator!=` now become disabled if the value,
error and exception types do not implement the same operator.
    - Relatedly, both comparison operators simply didn't work right. Fixed.
- [#109](
    - `swap()` now has correct `noexcept` calculation and now correctly
orders the swaps to be whichever is the throwing swap first.
- Added reference dump of v2.1 ABI so we can check if ABI breakage
detection works in the next set of changes, plus Travis job to check ABI
and API compatibility per commit.
- [#124](
    - `OUTCOME_TRY` is now overloaded and selects `void` or `auto`
edition according to input parameter count.
- [#120](
    - Fix generation of double underscored temporary variables in
    `OUTCOME_UNIQUE_NAME`, which is UB.
- [#110](
    - Separated `result` from its hard coded dependency on the
`<system_error>` header.
    - Renamed `result` and `outcome` to `basic_result` and `basic_outcome`.
    - Renamed `result.hpp` into `basic_result.hpp`.
    - Moved `<system_error>` and `<exception>` dependent code into new
`std_result.hpp` and `std_outcome.hpp` header files.
    - Added `boost_result.hpp` and `boost_outcome.hpp` which use
Boost.System and Boost.Exception (these are `result.hpp` and
`outcome.hpp` in the Boost edition).
ned Productions Limited Consulting

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