## PropertyTag

A Property Tag is a type used to name or identify properties that are attached to the vertices and edges of a graph. A Property type is not the type of the actual property values. Objects of the Property type are not used except to carry the type information which specifies the property. See the section about Custom Edge Properties for a description of how to define your own property tags.

### Associated Types

Property Kind | `property_kind<PropertyTag>::type` | This specifies whether the property is a Vertex Property Tag (`vertex_property_tag`), an Edge Property Tag (`edge_property_tag`), or a Graph Property Tag which is attached to the graph object itself (`graph_property_tag`). The tags are defined in `boost/graph/properties.hpp`. The `property_kind` traits class is defined in `boost/pending/property.hpp`.
Property ID Number | `property_num<PropertyTag>::value` | This is needed as a workaround when using compilers that do not support partial specialization (and hence prevent us from using `boost::is_same` to detect if two property tags are the same). The `property_num` traits class is defined in `boost/pending/property.hpp`.

### Refinement of

Default Constructible

### Models

The following models of the Property Tag concept are defined in `boost/graph/properties.hpp`.

- `vertex_index_t`
- `edge_index_t`
- `graph_name_t`
- `vertex_name_t`
- `edge_name_t`
- `edge_weight_t`
- `vertex_distance_t`
- `vertex_color_t`
- `vertex_degree_t`
- `vertex_out_degree_t`
- `vertex_in_degree_t`
- `vertex_discover_time_t`
- `vertex_finish_time_t`

### See Also

PropertyGraph and Property Map Concepts

### Notes

On compilers that do not support partial specialization, each Property type is also required to specialize `property_num<PropertyTag>` to contain an enum named `value` which uniquely identifies the property type.

Copyright © 2000-2001 | Jeremy Siek, Indiana University (jsiek@osl.iu.edu)