Hi,
An essential question: Should boost::lambda::constructor<int>()("") compiles?
Definitely no.
I have crafted a general replacement of T(a) as a workaround for dangerous conversions caused by T(a) which may happen in some kinds of templates.
There is already one in boost (Functional/Factory) AFAIK, but it might has the same problem: http://www.boost.org/doc/libs/1_47_0/libs/functional/factory/doc/html/index.... boost::value_factory<T>()(arg1,arg2,arg3) // same as T(arg1,arg2,arg3)
To avoid the unexpected conversion, I first proposed use of T{...} . But it is not a perfect solution because it changes the meaning in some cases like std::vector<int>. But this is exactly the use-case T{...} was made for. Of course initializer_lists make this approach completely unusable...
Another possible solution would be to use static_cast<T>(a) for one constructor-argument, as static_cast is type-safe.
As shown in the top of this message, I picked boost::lambda::constructor as a concrete example, and verified that the problem really exists in the wild.
Not if lambda::constructor was well written, but it's hard to take care of all these pitfalls (typical C++).
Thinking more, I wonder why such dangerous conversion was explicitly injected to T(a) in the first place. I first thought of some C-compatibility issues. But now I think it cannot be, because T(a) is a new construct in C++. Is it possible to remove this dangerous conversion path in a future revision of the standard?
T(a) is a function-style cast which was used in C, removing it would be rather difficult. HTH michi7x7