Vladimir Batov wrote:
Matthew Chambers <matt.chambers42 <at> gmail.com> writes:
Did you ever use boost.convert on a non-defaultable type? I've never needed that.
It might come a surprise but non-defaultable types are the overwhelming majority of our classes. Easily 9:1. And I'd like to stress *our* classes and not just wacko-Vladimir's. And, yes, 'convert' is used well beyond ints and the like. The direction class in 'convert' documentation is a real class and we have plenty of similar ones not to mention considerably more complex. An enumerator as simple as
enum hamlet_problem { to_be, not_to_be };
has no default. I am not sure if extending the above to
But is an enum IStreamable? Aren't you relying on implicit conversion to/from int for streaming? An int *is* default constructable. hamlet_problem shroedinger = static_cast<hamlet_problem>(xxx_cast<int>(s,0));
enum hamlet_problem { to_be, not_to_be, i_dont_know };
will be helpful for poor Hamlet. From the design perspectives adding elements not relevant to the domain (i_dont_know) is pollution.
Hey, I just successfully compiled: int main() { enum X { y = 1, z = 2 }; X x; } on MSVC8, XCode gcc4.0.1 and Codewarrior 3.2.5. So doesn't: hamlet_problem shroedinger = xxx_cast<hamlet_problem>(s,to_be); just work? I expect this standard, given the C-language lineage.
I won't be surprised if you find a lot of non-defaultable types if you look closely around without pre-disposition that any class is supposed to have the default constructor. One needs to remember that the default constructor was introduced in C++ (if my memory serves me) so that objects would not be in an invalid state like 'int i;' can be. If one introduces the default constructor which does not, in fact, construct a valid object, then it seems to defeat the purpose.
Just as another data point, looking at *our* classes, I see many more types that are not IStreamable, but are default-constructable. In looking at my own types, those that are not default-constructable would not make sense to be IStreamable. The types I find that are non-default-constructable tend to hold references to items passed as a ctor args. I'm not opposed to supporting non-default-constructable types, I'm opposed to paying the cost of a more complicated interface to support them. Jeff