The Boost Parameter Library Reference Documentation 
| Author: | David Abrahams |
|---|---|
| Author: | Daniel Wallin |
| Contact: | dave@boost-consulting.com, dalwan01@student.umu.se |
| Organization: | Boost Consulting |
| Date: | 2005-07-17 |
| Copyright: | Copyright David Abrahams, Daniel Wallin 2005. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
class template keyword
- Defined in
- boost/parameter/keyword.hpp
- Models
- KeywordExpression
template <class Tag>
struct keyword
{
template <class T>
ArgumentPack operator=(T& value) const;
template <class T>
ArgumentPack operator=(T const& value) const;
template <class T>
ArgumentPack operator|(T& default_) const;
template <class T>
KeywordDefaultExpression operator|(T const& default_) const;
template <class F>
KeywordDefaultExpression operator||(F const&) const;
};
operator=
template <class T> ArgumentPack operator=(T& value) const; template <class T> ArgumentPack operator=(T const& value) const;
- Requires
- Nothing.
- Throws
- Nothing
- Returns
- A model of ArgumentPack, holding value (by reference), and tagged with Tag.
operator|
template <class T> KeywordDefaultExpression operator|(T& x) const; template <class T> KeywordDefaultExpression operator|(T const& x) const;
- Throws
- Nothing
- Returns
- An object that holds x as a default for the keyword tag Tag.
operator||
template <class F> KeywordDefaultExpression operator||(F const& fn) const;
- Throws
- Nothing
- Requires
- F is a nullary function object.
In the next two tables, fn is an object of type F.
- Returns
- An object that holds a reference to fn as a lazy default for the keyword tag Tag.
class template parameters
- Defined in
- boost/parameter/parameters.hpp
template <class P0, class P1, …, class PN>
struct parameters
{
template <class T0, class T1, …, class TN>
struct match
{
typedef … type;
};
template <class A0>
ArgumentPack operator()(A0 const& a0) const;
template <class A0, class A1>
ArgumentPack operator()(A0 const& a0, A1 const& a1) const;
template <class A0, class A1, …, class AN>
ArgumentPack operator()(A0 const& a0, A1 const& a1, …, AN const& aN) const;
};
Template Parameter Semantics
<P0, …, PN> are models of ParameterSpec. If Px is not an instance of either optional or required, it is treated as a keyword tag with the same meaning as optional<Px>.
match
Used to remove a function from overload resolution using SFINAE.
template <class T0, class T1, …, class TN> struct restrict { typedef … type; };
- Returns
- If the supplied argument types <T0, …, TN> fulfill the requirments of the specified ParameterSpec's, match<T0, …, TN>::type exists and is constructible from parameters<P0, …, PN>. Otherwise restrict<T0, …, TN>::type doesn't exist.
operator()
template <class A0> ArgumentPack operator()(A0 const& a0) const; template <class A0, class A1> ArgumentPack operator()(A0 const& a0, A1 const& a1) const; …
- Throws
- Nothing
- Returns
- A composite ArgumentPack containing all arguments <A0, …, AN>. If Ax is not a model of ArgumentPack, it is transformed into one by tagging the argument with the ParameterSpec Px in it's position.
class templates optional, required
- Models
- ParameterSpec
- Defined in
- boost/parameter/parameters.hpp
template <class Tag, class Predicate = unspecified> struct optional; template <class Tag, class Predicate = unspecified> struct required;
class template binding
- Defined in
- boost/parameter/binding.hpp
A metafunction that, given an ArgumentPack, returns the reference type of the parameter identified by Keyword. If no such parameter has been specified, returns Default.
template <class Parameters, class Keyword, class Default = unspecified>
struct binding
{
typedef … type;
};
class template lazy_binding
- Defined in
- boost/parameter/binding.hpp
A metafunction that, given an ArgumentPack, returns the reference type of the parameter identified by Keyword. If no such parameter has been specified, returns the type returned by invoking DefaultFn.
template <class Parameters, class Keyword, class DefaultFn>
struct lazy_binding
{
typedef … type;
};
Requirements
DefaultFn is a nullary function object. The type returned by invoking this function is determined by boost::result_of<DefaultFn()>::type on compilers that support partial specialization. On less compliant compilers a nested DefaultFn::result_type is used instead.
concept KeywordExpression, KeywordDefaultExpression
Models of these concepts are used as indices in a ArgumentPack. Models of KeywordDefaultExpression will hold a default value to be used when no appropriate argument was passed.
Lazy Defaults
A KeywordDefaultExpression may contain a lazy default, meaning it's default value is only computed when needed.
concept ArgumentPack
Models of this concept are containers of parameters where each parameter is tagged with a keyword.
Requirements
- x and z are objects that model ArgumentPack.
- z is a ArgumentPack containing only one argument, as created by keyword::operator.
- y is a model if KeywordExpression.
- u is a model if KeywordDefaultExpression.
- X is the type of x.
- K is the tag type used in y and u.
- D is the type of the default value in u.
| Expression | Type | Requirements | Semantics/Notes |
|---|---|---|---|
| x[y] | binding<X, K>::type | An argument tagged with K exists in x. | Returns the bound argument tagged with K. |
| x[u] | binding<X, K, D>::type | - | Returns the bound argument tagged with K if such an argument exists. Otherwise returns the default value of u. If u has a lazy default, this may throw whatever the default value function of u throws when x does not contain an argument tagged with K. |
| x, z | Model of ArgumentPack | - | Returns a composite ArgumentPack that contains bindings to all arguments bound in x and z. |
concept ParameterSpec
Used to describe type restrictions and positional meaning in a parameter set.
Models of this concept with special meaning are:
- required
- optional
Any other type will be treated as a keyword Tag.
macro BOOST_PARAMETER_KEYWORD
- Defined in
- boost/parameter/keyword.hpp
Macro used to define keyword objects.
BOOST_PARAMETER_KEYWORD(tag_namespace, name)
Requirements
- tag_namespace is the namespace where the tag-types will be placed.
- name is the name that will be used for the keyword.
macro BOOST_PARAMETER_FUN
- Defined in
- boost/parameter/macros.hpp
BOOST_PARAMETER_FUN(ret, name, lo, hi, parameters)
Requirements
- ret is the return type of the function.
- name is the name of the function.
- lo, hi defines the range of arities for the function.
- parameters is the name of the parameters<> instance used for the function.