Struct template expr

boost::proto::expr — Representation of a node in an expression tree.

Synopsis

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

template<typename Tag, typename Args, long Arity = Args::arity> 
struct expr {
  // types
  typedef Tag                                   proto_tag;         
  typedef Args                                  proto_args;        
  typedef mpl::long_< Arity >                   proto_arity;       
  typedef proto::default_domain                 proto_domain;      
  typedef proto::basic_expr< Tag, Args, Arity > proto_grammar;     
  typedef expr                                  proto_base_expr;   
  typedef expr                                  proto_derived_expr;
  typedef typename Args::childN                 proto_childN;        // For each N in [0,max(Arity,1)).

  // member classes/structs/unions
  template<typename Signature> 
  struct result {
    // types
    typedef unspecified type;
  };

  // public static functions
  template<typename... A> static expr const make(A const &...);

  // public member functions
  expr & proto_base();
  expr const & proto_base() const;
  template<typename A> unspecified operator=(A &);
  template<typename A> unspecified operator=(A const &);
  template<typename A> unspecified operator=(A &) const;
  template<typename A> unspecified operator=(A const &) const;
  template<typename A> unspecified operator[](A &);
  template<typename A> unspecified operator[](A const &);
  template<typename A> unspecified operator[](A &) const;
  template<typename A> unspecified operator[](A const &) const;
  template<typename... A> unspecified operator()(A const &...);
  template<typename... A> unspecified operator()(A const &...) const;

  // public data members
  proto_childN childN;  // For each N in [0,max(Arity,1)).
  static const long proto_arity_c;  // = Arity;
};

Description

proto::expr<> is a node in an expression template tree. It is a container for its child sub-trees. It also serves as the terminal nodes of the tree.

Tag is type that represents the operation encoded by this expression. It is typically one of the structs in the boost::proto::tag namespace, but it doesn't have to be. If Arity is 0 then this expr<> type represents a leaf in the expression tree.

Args is a list of types representing the children of this expression. It is an instantiation of one of proto::list1<>, proto::list2<>, etc. The child types must all themselves be either proto::expr<> or proto::basic_expr<>& (or extensions thereof via proto::extends<> or BOOST_PROTO_EXTENDS()), unless Arity is 0, in which case Args must be proto::term<T>, where T can be any type.

proto::expr<> is a valid Fusion random-access sequence, where the elements of the sequence are the child expressions.

`expr` public static functions

template<typename... A> static expr const make(A const &... a);

Requires:	The number of supplied arguments must be `max(Arity,1)`.
Returns:	A new `expr` object initialized with the specified arguments.

`expr` public member functions

```
expr & proto_base();
```
Returns:

*this
```
expr const & proto_base() const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator=(A & a);
```
Lazy assignment expression

Returns:

A new expression node representing the assignment operation.
```
template<typename A> unspecified operator=(A const & a);
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator=(A & a) const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator=(A const & a) const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator[](A & a);
```
Lazy subscript expression

Returns:

A new expression node representing the subscript operation.
```
template<typename A> unspecified operator[](A const & a);
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator[](A & a) const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename A> unspecified operator[](A const & a) const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
```
template<typename... A> unspecified operator()(A const &... a);
```
Lazy function call

Returns:

A new expression node representing the function call operation.
```
template<typename... A> unspecified operator()(A const &... a) const;
```
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.