On Fri, Feb 6, 2009 at 17:01, Vladimir Batov <batov@people.net.au> wrote:
I sympathize with the idealistic desire for lexical_cast to look like the dynamic_cast et al. The problem is that no matter how you make lexical_cast look it does not do what other language-supported casts do -- dynamic_cast el al work with *types*, lexical_cast works with *values*. Making lexical_cast look like what it is not (the "real" casts) has no practical value and is just misleading.
I have no idea what you mean by dynamic_cast working with "types" not "values". static_cast<float>(1000000000u) drastically changes the representation and the type, just like lexical_cast<float>("1000000000") does. And optional<> is not that strange. The first example in its documentation is "optional return values" ( http://www.boost.org/doc/libs/1_37_0/libs/optional/doc/html/boost_optional/e... ), which is exactly what attempt_lexical_cast<T>(x) just calling lexical_cast<optional<T> >(x) makes perfect sense to me, though it's so trivial that it seems like a waste to provide the extra function. Having the different semantics for the different type is just like dynamic_cast, just this one uses optional instead of *. One very clear use: if (optional<int> oi = lexical_cast<optional<int> >(mystring)) { int i = *oi; ... use i ... } else { ... parse failed ... } And if you want defaults: int i = -1; if (optional<int> oi = lexical_cast<optional<int> >(mystring)) { i = *oi; } ... use i ... Or, using the helper: int i = lexical_cast<optional<int> >(mystring).get_value_or(-1); Why is this so bad?