[Boost-users] [multiprecision] noexcept() usage in gmp int

Subject: [Boost-users] [multiprecision] noexcept() usage in gmp int
From: Francesco Biscani (bluescarni_at_[hidden])
Date: 2013-06-13 15:32:47

Hello,

I was trying out the new multiprecision library (kudos!), and I ran into a
problem. In order to make certain guarantees in my code regarding exception
safety, I am mandating that types being used in generic containers are
marked noexcept() for certain basic operations (namely, destruction and
move operations).

It seems like this is generally guaranteed in the multiprecision library
(tried with cpp_int and the mpfr adaptor), with the important exception of
the gmp integer class. A glance at the headers reveals that (gmp.hpp):

//
// Within this file, the only functions we mark as noexcept are those that
manipulate
// (but don't create) an mpf_t.  All other types may allocate at pretty
much any time
// via a user-supplied allocator, and therefore throw.
//

Additionally, browsing the gmp documentation yields this snippet (
http://gmplib.org/manual/Custom-Allocation.html):

"""
There's currently no defined way for the allocation functions to recover
from an error such as out of memory, they must terminate program execution.
A longjmp or throwing a C++ exception will have undefined results. This may
change in the future.
"""

Would it be possible then for the mp library authors to consider adding
basic noexcept() guarantees to the gmp adaptor class in future versions?

Cheers and thanks for the great library,

  Francesco.