Readable Property Map
A Readable Property Map provides the get() function to obtain the value associated with a key.
Refinement of
Copy Constructible
Notation
PMap |
A type that is a model of Readable Property Map. |
pmap |
An object of type PMap. |
key |
An object of type boost::property_traits<PMap>::key_type. |
Associated Types
Value Type |
boost::property_traits<PMap>::value_type |
|
Key Type |
boost::property_traits<PMap>::key_type |
|
Reference Type |
boost::property_traits<PMap>::reference |
value_type must be constructible by reference. |
Property Map Category |
boost::property_traits<PMap>::category |
Must convertible to
boost::readable_property_map_tag.
|
Valid Expressions
Name | Expression | Return Type | Description |
Get Property Value |
get(pmap, key) |
boost::property_traits<PMap>::reference |
Lookup the value associated with key. |
Concept Checking Class
template <class PMap, class Key>
struct ReadablePropertyMapConcept
{
typedef typename property_traits<PMap>::key_type key_type;
typedef typename property_traits<PMap>::category Category;
typedef boost::readable_property_map_tag ReadableTag;
void constraints() {
function_requires< ConvertibleConcept<Category, ReadableTag> >();
val = get(pmap, k);
}
PMap pmap;
Key k;
typename property_traits<PMap>::value_type val;
};
See Also
Property map concepts - Writable Property Map - Read / Write Property Map - Lvalue Property Map - Mutable Lvalue Property Map
Design Notes
At various times the name "read-only" was considered for
this concept. However, that name is inappropriate because concepts are
inherently positive, not negative. This becomes obvious when we define
the Read Write Property Map, which refines both the Readable Property
Map and the Writable Property Map concept. It would not make much
sense to combine "read-only" and "write-only"
concepts!