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Subject: Re: [boost] [outcome] Second high level summary of review feedback accepted so far
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-30 19:36:42

>> I currently, roughly speaking, find approx 50% in favour of a runtime
>> checked edition, approx 40% in favour of a statically checked edition.
>> Emil and Vicente make up the 10% of folk who want something completely
>> different.
> It is probably not a good idea to measure correctness by popular opinion,

I think C++ Either result types will always fall into two camps, narrow
and wide. As you mentioned yourself Emil, the cause is the language's
current inability to specify statically correctness preconditions for
function calls. That would get a lot better if something like Herb's
metaclasses came along, but those are many, many years out, if ever.

Until then we are trapped: either put UB on the observers so it can be
trapped at compile time, or eliminate all UB so logic errors appear at
runtime. You can choose either of those per function, but you cannot
have both at once per function.

I intend to put UB "raw" observers on the runtime checked editions,
maybe using the form Peter suggested. But I am deeply opposed to having
short-to-type-out observers like operator*() do UB unless the type's
name loudly declares "I am an unsafe type".


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