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Subject: Re: [boost] [Range] New I/O functions for ranges
From: Nat Goodspeed (nat_at_[hidden])
Date: 2014-11-24 11:03:11

On Wed, Oct 15, 2014 at 7:38 PM, Indiana <[hidden]> wrote:

> The only way to prevent binding to temporaries in C++98 is to take arguments
> by non-const (lvalue) reference, but if write_all() does that then the "as
> lvalue" code above won't work.
> So my options come down to this:
> 1) Declare the library C++11-or-better-only. That can be enforced by
> ensuring that BOOST_NO_CXX11_RVALUE_REFERENCES is not defined, and issuing
> an error message otherwise.
> 2) Allow the library to be used in C++98 code, with a warning - either in
> documentation or, less than ideally, as a diagnostic - about temporaries.
> Note that there is no way to detect or diagnose if the warning is ignored,
> deliberately or accidentally, so things that are perfectly legal in C++11
> mode can silently introduce undefined behaviour in C++98 mode.

A third potential option would be to restrict the API based on
BOOST_NO_CXX11_RVALUE_REFERENCES. That is, when that macro is set,
make write_all() accept non-const reference. This could potentially
allow *some* use of the library even with C++03 code -- say, with a
local vector -- without loss of safety.

> I don't think it's a worthwhile to introduce potentially undetectable
> bugs. Better to say "if you can't use it safely, you can't use it"

I agree with the above. I simply suggest that even in C++03, you could
potentially support a safe subset of desirable use cases.

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