Thanks Gustaf and Artur!
Not sure if this should be considered expected behaviour - but does the type have to be defined before declaration? This simple script illustrates the issue - see the last couple of attempts.
Class Base -slots { Attribute connects_to -multivalued true -type Base } Class DerivedA -superclass Base -slots { Attribute connects_to -multivalued true -type DerivedB } Class DerivedB -superclass Base -slots { Attribute connects_to -multivalued true -type DerivedA }
Base b DerivedA da DerivedB db
b connects_to add da b connects_to add db
db connects_to add b
can't set "connects_to": b is not of type DerivedA << This should be
expected. all A-ok.
db connects_to add da da connects_to add b
can't set "connects_to": bad class "DerivedB": must be alnum, alpha,
ascii, control, boolean, digit, double, false, grap h, integer, lower, print, punct, space, true, upper, wordchar, or xdigit
da connects_to add db
can't set "connects_to": bad class "DerivedB": must be alnum, alpha,
ascii, control, boolean, digit, double, false, grap h, integer, lower, print, punct, space, true, upper, wordchar, or xdigit
On Nov 7, 2007 12:06 AM, Gustaf Neumann neumann@wu-wien.ac.at wrote:
Shishir Ramam schrieb:
Hi, I have a need to represent a directed graph in XoTcl.
Here are two small examples for representing graphs
In version one, edges are lists of references to nodes stored as attributes of nodes. By specifying "-multivalued true", it is possible to "add" or "delete" elements from the list. By using "-type Node" the code ensures, that only instances of Node may be added to the list, otherwise an error is thrown.
Class Node -slots { Attribute connects_to -multivalued true -type Node }
Node n1 Node n2 Node n3
n1 connects_to add n2 n1 connects_to add n3
puts [n1 connects_to]
A "destroy" of a nodes automatically destroys the edges as well, by refining the destroy method, one could as well destroy the referenced edges (similar to aggregation (nesting objects), but one has to be care about cyclical edges.
Another approach is to define Edges as objects which makes it possible to provide methods for Edges and to store attributes in it.
Class Edge -slots { Attribute from -type Node Attribute to -type Node }
Edge e1 -from n1 -to n2 Edge e2 -from n1 -to n3
Simarly as above, when a dynamic graph is to be maintained, the destroy method of Node should care about deleting references in Edges to ensure referencial integrity. The easiest way is to check in the destroy method of Node all Edges with [Edge info instances], if their "form" or "to" attributes contain the node. One could as well build an index to make this operation faster for large graph via a constructor of Edge, which maintains e.g. a list of referenced edges per node (e.g. via multivalued attribute "references", similar to approach 1)
-gustaf neumann