AMDG Johannes Stallkamp wrote:
Hello there,
Short version: Are there any reasons, why base class access is currently not allowed/implemented in boost::function (via target() function)?
Short answer: It's not at all easy to implement.
Long version/explanation/scenario:
Long answer: Boost.Function stores a pointer, but it's a void pointer so it loses all type information. The type information is stored separately, using std::type_info. With this setup, there is no way to determine whether the type that you ask for is a base of the stored type. The only way to implement this is to create a class the inherits multiply from the stored type and a common base. This allows the use of dynamic_cast to cross cast. This unfortunately requires that it be possible to derive from the stored type, so built-ins become a special case. In addition, it makes the small buffer optimization difficult to implement seriously hurting performance even when this feature is not used. In Christ, Steven Watanabe