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[SVN r40832]
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Joel de Guzman
2007-11-06 12:13:52 +00:00
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doc/extension.qbk
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@ -1,9 +1,9 @@
[section Extension]
[section The Full Extension Mechanism]
[section:ext_full The Full Extension Mechanism]
The Fusion library is designed to be extensible, new sequences types can easily
be added. In fact, the library support for `std::pair`, `boost::array` and __mpl__
be added. In fact, the library support for `std::pair`, `boost::array` and __mpl__
sequences is entirely provided using the extension mechanism.
The process for adding a new sequence type to Fusion is:
@ -30,7 +30,7 @@ are going to use the type:
{}
};
}
We are going to pretend that this type has been provided by a 3rd party
library, and therefore cannot be modified. We shall work through all the
necessary steps to enable `example_struct` to serve as an __associative_sequence__
@ -54,7 +54,7 @@ tag type for operations involving our sequence. This is done by specializing
#include <boost/fusion/support/tag_of_fwd.hpp>
#include <boost/fusion/include/tag_of_fwd.hpp>
namespace boost { namespace fusion { namespace traits {
namespace boost { namespace fusion { namespace traits {
template<>
struct tag_of<example_struct>
{
@ -62,8 +62,8 @@ tag type for operations involving our sequence. This is done by specializing
};
}}}
`traits::tag_of` also has a second template argument,
that can be used in conjuction with `boost::enable_if` to provide tag
`traits::tag_of` also has a second template argument,
that can be used in conjuction with `boost::enable_if` to provide tag
support for groups of related types. This feature is not necessary
for our sequence, but for an example see the code in:
@ -100,7 +100,7 @@ A quick summary of the details of our iterator:
# The iterator is parameterized by the type it is iterating over, and the index of the current element.
# The typedefs `struct_type` and `index` provide convenient access to information we will need later in
the implementation.
# The typedef `category` allows the `traits::__category_of__` metafunction to establish
# The typedef `category` allows the `traits::__category_of__` metafunction to establish
the traversal category of the iterator.
# The constructor stores a reference to the `example_struct` being iterated over.
@ -113,7 +113,7 @@ add features to our implementation.
[heading A first couple of instructive features]
To start with, we will get the __result_of_value_of__ metafunction working. To
do this, we provide a specialization of the `boost::fusion::extension::value_of_impl` template for
do this, we provide a specialization of the `boost::fusion::extension::value_of_impl` template for
our iterator's tag type.
template<>
@ -188,7 +188,7 @@ specialization of `deref_impl`.
}
The use of `deref_impl` is very similar to that of `value_of_impl`, but it also
provides some runtime functionality this time via the `call` static member function.
provides some runtime functionality this time via the `call` static member function.
To see how `deref_impl` is used, lets have a look at the implementation of __deref__:
namespace result_of
@ -213,7 +213,7 @@ same way as the __value_of__ implementation. The runtime functionality used
by __deref__ is provided by the `call` static function of the selected
__mpl_metafunction_class__.
The actual implementation of `deref_impl` is slightly more complex than that of `value_of_impl`.
The actual implementation of `deref_impl` is slightly more complex than that of `value_of_impl`.
We also need to implement the `call` function, which returns a reference
to the appropriate member of the underlying sequence. We also require a little
bit of metaprogramming to return `const` references if the underlying sequence
@ -261,7 +261,7 @@ __random_access_iterator__ `distance_impl` and `advance_impl` also need to be pr
in order to satisfy the necessary complexity guarantees. As our iterator is
a __random_access_iterator__ we will have to implement all of these functions.
Full implementations of `prior_impl`, `advance_impl`, `distance_impl` and `equal_to_impl` are
Full implementations of `prior_impl`, `advance_impl`, `distance_impl` and `equal_to_impl` are
provided in the example code.
[heading Implementing the intrinsic functions of the sequence]
@ -279,7 +279,7 @@ an `impl` type specialized for our sequence tag:
We've some similar formalities to complete, providing `category_of_impl` so Fusion
can correctly identify our sequence type, and `is_view_impl` so Fusion can correctly
identify our sequence as not being a __view__ type. Implementations are
identify our sequence as not being a __view__ type. Implementations are
provide in the example code.
Now we've completed some formalities, on to more interesting features. Lets get
@ -304,7 +304,7 @@ our sequence.
The implementation uses the same ideas we have applied throughout, in this case
we are just creating one of the iterators we developed earlier, pointing to the
first element in the sequence. The implementation of __end__ is very similar, and
first element in the sequence. The implementation of __end__ is very similar, and
is provided in the example code.
For our __random_access_sequence__ we will also need to implement `size_impl`,
@ -312,10 +312,10 @@ For our __random_access_sequence__ we will also need to implement `size_impl`,
[heading Enabling our type as an associative container]
In order for `example_struct` to serve as an associative container,
In order for `example_struct` to serve as an associative container,
we need to enable 3 lookup features, __at_key__, __value_at_key__ and __has_key__.
We also need to provide an implementation of the `is_associative` trait
so that our sequence can be correctly identified as an associative container.
so that our sequence can be correctly identified as an associative container.
To implement `at_key_impl` we need to associate the `fields::age` and `fields::age`
types described in the __quick_start__ guide with the appropriate members of `example_struct`.
@ -465,7 +465,7 @@ The user must the implement the key expressions required by their iterator type.
[section Macros]
[section BOOST_FUSION_ADAPT_STRUCT]
[section:adapt_struct BOOST_FUSION_ADAPT_STRUCT]
[heading Description]
BOOST_FUSION_ADAPT_STRUCT is a macro that can be used to generate all the
@ -515,7 +515,7 @@ namespace qualified name of the struct to be converted.
[endsect]
[section BOOST_FUSION_ADAPT_ASSOC_STRUCT]
[section:adapt_assoc BOOST_FUSION_ADAPT_ASSOC_STRUCT]
[heading Description]
BOOST_FUSION_ADAPT_ASSOC_STRUCT is a macro that can be used to generate all the
@ -539,9 +539,9 @@ and __associative_sequence__.
)
The above macro generates the necessary code to adapt `struct_name`
as a model of __random_access_sequence__ and __associative_sequence__.
as a model of __random_access_sequence__ and __associative_sequence__.
The sequence of `(member_typeN, member_nameN, key_typeN)`
triples declare the type, name and key type of each of the struct members
triples declare the type, name and key type of each of the struct members
that will be part of the sequence.
The macro should be used at global scope, and `struct_name` should be the fully