The $_g reserved variable

[Marko A. Rodriguez]

Hi everyone,

The Gremlin function library comes with a set of graph functions [ http://wiki.github.com/tinkerpop/gremlin/gremlin-function-library#graph_functions ]. All of these graph functions require the first argument to be a graph object. In order to make the call to these functions more concise, I have created a new reserved variable called $_g. This variable can only be set to an object that implement the Graph.java interface.

Now, this $_g variable can be assigned a graph and in such cases, it is not required to provide a graph parameter to any graph functions in the Gremlin function library or elsewhere (e.g. Sesame function library). Here are some examples of how it works:

         \,,,/

         (o o)

-----oOOo-(_)-oOOo-----

gremlin> $_g := tg:open()

==>tinkergraph[vertices:0]

gremlin> g:load('src/test/resources/com/tinkerpop/gremlin/model/parser/graph-example-1.xml')

==>true

gremlin> $_ := g:id('1')

==>v[1]

gremlin> $v := g:key('name','marko')[1]

==>v[1]

gremlin> g:add-v()

==>v[0]

gremlin> g:add-v()

==>v[7]

gremlin> $_g/V

==>v[3]

==>v[2]

==>v[1]

==>v[0]

==>v[7]

==>v[6]

==>v[5]

==>v[4]

gremlin> g:add-e(g:add-v(), 'respects', g:add-v())

==>e[10][8-respects->9]

gremlin> $_g/E

==>e[7][1-knows->2]

==>e[9][1-created->3]

==>e[8][1-knows->4]

==>e[12][6-created->3]

==>e[10][4-created->5]

==>e[11][4-created->3]

==>e[10][8-respects->9]

gremlin> g:clear()

==>true

gremlin> $_g

==>tinkergraph[vertices:0]

gremlin> 

Finally, I added the reserved variable to the wiki Cheat Sheet [ http://wiki.github.com/tinkerpop/gremlin/cheat-sheet ].

Hopefully this makes it "cleaner" to code in Gremlin.

Take care,

Marko.

http://markorodriguez.com

http://tinkerpop.com