[PATCH] streambuf_iterator: avoid debug-dependent behaviour

[François Dumont]

Hi

     You should perhaps justify why you want to do those changes.

On 24/08/2017 11:57, Petr Ovtchenkov wrote:
> Explicit do sgetc from associated streambuf. Avoid debug-dependent
> sgetc (within _M_at_eof()):
>
>         __glibcxx_requires_cond(!_M_at_eof(),
>                                 _M_message(__gnu_debug::__msg_inc_istreambuf)
>                                 ._M_iterator(*this));
>
> Increment operators not require not-eof precoditions.
>
> Don't unlink associated streambuf if eof detected (in _M_get).

Why ? Are you working with a streambuf_type implementation that can 
return eof at some moment and later return something else ?

I don't think istreambuf_iterator has been designed to work with such a 
streambuf_type implementation. Your streambuf_type should block until it 
fetches data, just do it in a background thread if you don't want to 
block all your application while waiting for it.

However your request made me consider this implementation, I wonder why 
it is done this way. Especially why the mutable keywords ?

I would have expected an implementation more consistent with the 
istream_iterator implementation reading current character on 
construction like in the attached patch.

Is it because of the _GLIBCXX_USE_NOEXCEPT constraint on the 
constructors ? Can sgetc() throw ?

François

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