###

# Boost.Python

## Header <boost/python/overloads.hpp>

## Contents

Introduction
overload-dispatch-expressions
OverloadDispatcher concept
Macros
  BOOST_PYTHON_FUNCTION_OVERLOADS
  BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS
Example(s)

## Introduction

Defines facilities for generating families of overloaded Python functions and extension class methods from C++ functions and member functions with default arguments, or from similar families of C++ overloads

## overload-dispatch-expressions

An overload-dispatch-expression is used to describe a family of overloaded methods to be generated for an extension class. It has the following properties:

> docstring: An ntbs whose value will bound to the methods' `__doc__` attribute
> keywords: A keyword-expression which will be used to name (a trailing subsequence of) the arguments to the generated methods.
> call policies: An instance of some type which models CallPolicies.
> minimum arity The minimum number of arguments to be accepted by a generated method overload.
> maximum arity The maximum number of arguments to be accepted by a generated method overload.

## OverloadDispatcher Concept

An OverloadDispatcher `X` is a class which has a minimum arity and a maximum arity, and for which the following following are valid overload-dispatch-expressions, with the same minimum and maximum arity as the OverloadDispatcher.

    X()
    X(docstring)
    X(docstring, keywords)
    X(keywords, docstring)
    X()[policies]
    X(docstring)[policies]
    X(docstring, keywords)[policies]
    X(keywords, docstring)[policies]

- If `policies` are supplied, it must be an instance of a type which models CallPolicies, and will be used as the result's call policies. Otherwise the result's call policies will be an instance of default_call_policies.
- If `docstring` is supplied it must be an ntbs, and will be used as the result's docstring. Otherwise the result has an empty docstring.
- If `keywords` is supplied it must be the result of a keyword-expression whose length is no greater than `X`'s maximum arity, and will be used as the result's keywords. Otherwise the result's keywords will be empty.

## Macros

### BOOST_PYTHON_FUNCTION_OVERLOADS(name, func_id, min_args, max_args)

Expands to the definition of an OverloadDispatcher called `name` in the current scope which can be used to generate the following function invocation:

    func_id(a1, a2,...ai);

for all `min_args` <= i <= `max_args`.

### BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(name, member_name, min_args, max_args)

Expands to the definition of an OverloadDispatcher called `name` in the current scope which can be used to generate the following function invocation:

    x.member_name(a1, a2,...ai);

for all `min_args` <= i <= `max_args`, where `x` is a reference to an object of class type.

## Example(s)

    #include <boost/python/module.hpp>
    #include <boost/python/def.hpp>
    #include <boost/python/args.hpp>
    #include <boost/python/tuple.hpp>
    #include <boost/python/class.hpp>
    #include <boost/python/overloads.hpp>
    #include <boost/python/return_internal_reference.hpp>

    using namespace boost::python;

    tuple f(int x = 1, double y = 4.25, char const* z = "wow")
    {
        return make_tuple(x, y, z);
    }

    BOOST_PYTHON_FUNCTION_OVERLOADS(f_overloads, f, 0, 3)

    struct Y {};
    struct X
    {
        Y& f(int x, double y = 4.25, char const* z = "wow")
        {
            return inner;
        }
        Y inner;
    };

    BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(f_member_overloads, f, 1, 3)

    BOOST_PYTHON_MODULE(args_ext)
    {
        def("f", f,
            f_overloads(
                args("x", "y", "z"), "This is f's docstring"
            ));

        class_<Y>("Y")
            ;

        class_<X>("X", "This is X's docstring")
            .def("f1", &X::f,
                    f_member_overloads(
                        args("x", "y", "z"), "f's docstring"
                    )[return_internal_reference<>()]
            )
            ;
    }

Revised 15 April, 2003

© Copyright Dave Abrahams 2002.