[Patch] libstdc++/16612

[Phil Edwards]

Hi Paolo!  Thanks for working so hard on this stuff.

If the stop-gap measure is going to take the form of a configury switch,
I would request two changes:

>  dnl
> +dnl Check for whether a fully dynamic basic_string implementation should be
> +dnl turned on (mostly useful together with shared_allocator).
> +dnl
> +dnl --enable-fully-dynamic-string defines _GLIBCXX_FULLY_DYNAMIC_STRING
> +dnl --disable-fully-dynamic-string leaves _GLIBCXX_FULLY_DYNAMIC_STRING undefined
> +dnl  +  Usage:  GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING[(DEFAULT)]
> +dnl       Where DEFAULT is either `yes' or `no'.
> +dnl
> +AC_DEFUN([GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING], [
> +  GLIBCXX_ENABLE(fully-dynamic-string,$1,,[enables fully dynamic basic_string])

The autoconf macro description ("Check for...") and the --help output string
are somewhat redundant and uninformative, given the name of the option.
That is, I expect "--enable-foo" to enable foo; a help string that says
"this enables foo" kind of falls short.  :-)

If they said something about "empty strings in per-process static memory,"
that would probably be enough.


> + <dt><code>--enable-fully-dynamic-string  </code></dt>
> + <dd><p>This option enables a special version of basic_string avoiding
> +        the optimization that allocates empty objects in static memory.
> +	Mostly useful together with shared memory allocators.
> +     </p>
> + </dd>

Could this, and maybe the autoconf macro description, either mention the PR
which started the whole thing, and/or link into the mailing list archives?
As it stands, a user reading these descriptions might legitimately wonder,
"under what conditions would I use this option, and do I need to use it now?"

If this is intended to be a temporary solution, that would probably be
mentioned as well.

What do you think?


Phil

-- 
AI.cpp:33241: warning: You wrote 'neurons.merge(solution1, solution2)",
AI.cpp:33241: you probably MEANT "neurons->merge(solution1, solution2)",
AI.cpp:33241: but there is a MUCH better way to implement this whole
AI.cpp:33241: function; doing that instead.