boost::proto::deduce_domain — A pseudo-domain for use in functions and metafunctions that require a domain parameter. It indicates that the domain of the parent node should be inferred from the domains of the child nodes.
proto::deduce_domain is used as a domain — either
explicitly or implicitly by
or Proto's operator overloads — Proto will use the domains of the child expressions to
compute the domain of the parent. It is done in such a way that (A) expressions in domains
that share a common super-domain are interoperable, and (B) expressions that are in
the default domain (or a sub-domain thereof) are interoperable with all
expressions. The rules are as follows:
proto::default_domainand all its sub-domains are weaker than all other domains.
proto::default_domainand U contains an element that is not
proto::default_domain, it is an error.
Note: the above description sounds like it would be expensive to compute at compile time. In fact, it can all be done using C++ function overloading.