Edward Diener wrote:
Can you give an example of the compile-time use of reflection for templates and how this would be done ? Or have I completely misunderstood what you and Sebastian Redl are discussing ?
Although this came up in a different branch of discussion, the topic of David and my discussion was about the hardships of implementing a solution that could, at run-time, instantiate a template and load the newly generated code into the application. But for an example of compile-time reflection, I posted something a few days ago, in the thread about a policy selector using a mpl vector of policy classes. There, I used the mpl utility macro BOOST_HAS_NAMED_TYPEDEF (I think is the name of the macro.) This is one very limited example of compile-time reflection. Real language support would allow for far more interesting things here. My example implemented this compile-time pseudo-code: metafunction type policy_type(type policy) { if(policy.has_typedef("policy_type")) { return policy.policy_type; } else { return not_a_policy; } } Overloads (= specializations) could be provided for types that had a policy_type but no nested typedef policy_type. The has_typedef would basically be a part of compile-time reflection. However, reflection would be far more powerful. Instead of just testing for the existence, you could for example enumerate all typedefs. Sebastian Redl