Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.

Struct template domain

boost::proto::domain — For use in defining domain tags to be used with proto::extends<>. A domain associates an expression type with a generator, and optionally a grammar.


// In header: <boost/proto/domain.hpp>

template<typename Generator = proto::default_generator, 
         typename Grammar = proto::_> 
struct domain :  Generator {
  // types
  typedef Grammar proto_grammar;


The Generator determines how new expressions in the domain are constructed. Typically, a generator wraps all new expressions in a wrapper that imparts domain-specific behaviors to expressions within its domain. (See proto::extends<>.)

The Grammar determines whether a given expression is valid within the domain, and automatically disables any operator overloads which would cause an invalid expression to be created. By default, the Grammar parameter defaults to the wildcard, proto::_ , which makes all expressions valid within the domain.


 template<typename Expr>
 struct MyExpr;

 struct MyGrammar
   : proto::or_< proto::terminal<_>, proto::plus<MyGrammar, MyGrammar> >

 // Define MyDomain, in which all expressions are
 // wrapped in MyExpr<> and only expressions that
 // conform to MyGrammar are allowed.
 struct MyDomain
   : proto::domain<proto::generator<MyExpr>, MyGrammar>

 // Use MyDomain to define MyExpr
 template<typename Expr>
 struct MyExpr
   : proto::extends<Expr, MyExpr<Expr>, MyDomain>
     // ...