On 5/3/2011 3:05 PM, John Bytheway wrote:
Finally, I am concerned by the prospect of ODR violations as a result of specialised conversions. Taking again the string-to-bool conversion as an example: if part of a program is compiled with this optimized implementation present, and part is compiled with it absent, then I suspect the program will be in violation of the ODR. This seems really quite dangerous. In particular, I see no safe way for me to write an optimized or otherwise customized implementation of any conversion unless either
(a) it is distributed as part of Boost.Convert, and included unconditionally whenever the definition of convert is, or
(b) it converts to or from a type A, and is included unconditionally whenever the definition of A is.
Is the extension facility intended to be used in these limited circumstances? If so, then that fact must also be clearly and conspicuously documented. If not, then I would like to know how ODR violations are to be avoided.
I use an optional header that defines lexical_cast string->numeric specializations using strto[ld]. Is this at risk for ODR violations? I use it widely but I'm not at all careful about making sure it's included everywhere. Yet I haven't had any ODR violations on GCC or MSVC. Unless that's pure luck, I'd like to know how the optional specializations are ODR violations. -Matt