On 16/08/11 15:59, Gordon Woodhull wrote:
Hi all,
The review of Vicente Botet Escriba's Conversion library starts this Saturday August 20 and continues through August 29.
This library provides a general system for type-to-type conversion. As such, it can be thought of either as a substitute for overloading static_cast, or as an alternative to lexical_cast when the intermediate conversion to text is not wanted.
Your review and/or discussion would be greatly appreciated. As always, please post to the main Boost list if possible, or the boost-users list, or you can send your review directly to the Review Managers.
The primary concern I always have with libraries such as this one is that they promote ODR violations. In particular, consider: library A defines type TA library B defines type TB library C defines a conversion from TA to TB library D defines a conversion from TA to TB Now libraries C and D are incompatible; they cannot both be used in the same program without ODR violation. This means, if I am writing a library, then I cannot safely define a conversion between types both of which are not in my library, because it would make my library incompatible with any other library that also defines such a conversion. But, on the other hand, if one of the types *is* in my library, then I can probably make do with a conversion constructor or conversion operator (except perhaps if I want an explicit conversion operator and want to support compilers without those). So, as I see it, conversions can only be defined in two situations: - When writing non-library code (i.e. code that will not be combined with other code over which the author has no control). - As a stop-gap substitute for explicit conversion operators. Is it indeed intended only to allow conversions to be defined in these limited circumstances? If so, then the documentation should state that clearly. If not, how do you intend to avoid ODR violations? John Bytheway