| 作者 | David Abrahams, Jeremy Siek, Thomas Witt |
|---|---|
| 联系方式 | dave@boost-consulting.com, jsiek@osl.iu.edu, witt@styleadvisor.com |
| 组织 | Boost Consulting, Indiana University 开放系统实验室, Zephyr Associates, Inc. |
| 日期 | 2006-09-11 |
| 版权 | Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2004. |
| 摘要 | 该iterator_archetype类构建了对迭代器访问概念和迭代器遍历概念之一的最小实现。它用于在编译时检查模板的类型要求是否足以覆盖模板的实现。更多信息请参阅 boost::concept_check 库的文档。 |
|---|
namespace iterator_archetypes
{
// Access categories
typedef /*implementation defined*/ readable_iterator_t;
typedef /*implementation defined*/ writable_iterator_t;
typedef /*implementation defined*/ readable_writable_iterator_t;
typedef /*implementation defined*/ readable_lvalue_iterator_t;
typedef /*implementation defined*/ writable_lvalue_iterator_t;
}
template <
class Value
, class AccessCategory
, class TraversalCategory
>
class iterator_archetype
{
typedef /* see below */ value_type;
typedef /* see below */ reference;
typedef /* see below */ pointer;
typedef /* see below */ difference_type;
typedef /* see below */ iterator_category;
};
提供的访问类别类型对应于以下标准迭代器访问概念组合
readable_iterator_t := Readable Iterator writable_iterator_t := Writeable Iterator readable_writable_iterator_t := Readable Iterator & Writeable Iterator & Swappable Iterator readable_lvalue_iterator_t := Readable Iterator & Lvalue Iterator writeable_lvalue_iterator_t := Readable Iterator & Writeable Iterator & Swappable Iterator & Lvalue Iterator
该AccessCategory参数必须是预定义的访问类别标签之一。TraversalCategory必须是标准遍历标签之一。值类型必须满足由以下指定的迭代器概念的要求AccessCategoryandTraversalCategory如嵌套特性类型所暗示的那样。
iterator_archetype实现了由以下指定的迭代器概念AccessCategoryandTraversalCategory参数。iterator_archetype不实现任何其他访问概念或更高级的遍历概念。
嵌套特性类型定义如下：
if (AccessCategory == readable_iterator_t)
value_type = Value
reference = Value
pointer = Value*
else if (AccessCategory == writable_iterator_t)
value_type = void
reference = void
pointer = void
else if (AccessCategory == readable_writable_iterator_t)
value_type = Value
reference :=
A type X that is convertible to Value for which the following
expression is valid. Given an object x of type X and v of type
Value.
x = v
pointer = Value*
else if (AccessCategory == readable_lvalue_iterator_t)
value_type = Value
reference = Value const&
pointer = Value const*
else if (AccessCategory == writable_lvalue_iterator_t)
value_type = Value
reference = Value&
pointer = Value*
if ( TraversalCategory is convertible to forward_traversal_tag )
difference_type := ptrdiff_t
else
difference_type := unspecified type
iterator_category :=
A type X satisfying the following two constraints:
1. X is convertible to X1, and not to any more-derived
type, where X1 is defined by:
if (reference is a reference type
&& TraversalCategory is convertible to forward_traversal_tag)
{
if (TraversalCategory is convertible to random_access_traversal_tag)
X1 = random_access_iterator_tag
else if (TraversalCategory is convertible to bidirectional_traversal_tag)
X1 = bidirectional_iterator_tag
else
X1 = forward_iterator_tag
}
else
{
if (TraversalCategory is convertible to single_pass_traversal_tag
&& reference != void)
X1 = input_iterator_tag
else
X1 = output_iterator_tag
}
2. X is convertible to TraversalCategory