[boost] Serialisation: Is is_trivial<T> a sufficient precondition to bypass serialisation?

Subject: [boost] Serialisation: Is is_trivial<T> a sufficient precondition to bypass serialisation?
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2015-02-04 06:54:56

A library user has raised an interesting question at:

https://github.com/BoostGSoC13/boost.afio/commit/ac32ebfceb9a08b133e8c
d47000d3b4807bc3e42#commitcomment-9574522

Basically, AFIO v1.3 has new pre-serialisation metaprogramming in 
response to Robert's comments on his Incubator about it being too 
hard to serialise and deserialise data with AFIO. AFIO will now 
consume any STL container and will implicitly auto expand to ASIO 
scatter gather buffers any:

1. Trivial type T
2. C array of trivial type T
3. STL container of trivial type T, including initializer_list.

A free function, to_asio_buffers(T), can be specialised by external 
code to extend this with custom ASIO scatter gather buffers 
generation. Note that AFIO explicitly and intentionally expects that 
anyone interested in async file i/o will be doing their serialisation 
and endian conversion far away from AFIO code, so to_asio_buffers(T) 
is really for marking extra types to be treated as implicit auto 
expand.

The user asks the question: Is is_trivial<T> a sufficient 
precondition for this auto expansion to be safe, or should 
is_standard_layout<T> also be required? The user notes that 
is_trivial<T> && is_standard_layout<T> == is_pod<T> which seems a 
little overkill to me.

There is also the possibility that is_trivial<T> is too conservative. 
Some may argue that is_trivially_copyable<T> would be sufficient. 
Thoughts?

Niall

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