[FR-devel] Added simple links in databus

[Rich Kilmer]

As the subject says, I added the ability to create simple links in the
databus between two paths.  So if you have a slot:

db = FreeBASE::DataBus.new
slot1 = db['slot1']

You can create a link to another path in the databus:

slot1.link("subslot1", "/slot2/subslot2")

Then if you access subslot1:

puts db['slot1/subslot1'].path #=> /slot2/subslot2

I also added:

slot1.is_linked?("subslot1") #=> true 

and

slot1.unlink("subslot1")

The reason I call this simple linking is that if you traverse a relative
path through a link you could have problems:

db = FreeBASE::DataBus.new
slot1 = db['slot1']
slot1.link('subslot1', 'slot2/subslot2')

and then you go:

x = db['slot1/subslot1/..']
puts x.path #=> /slot2

In other words, the links are a single (forward) direction.  Creating
something like symbolic links in Linux that maintain their reverse
direction would be very hard to do in the current databus architecture.

Why is this useful:

db = DataBus.new
db['/system/ui/component/pool/EditPane/pane1']
db['/system/ui/component/pool/EditPane/pane2']
db['/system/ui/component/pool/EditPane/pane2']
db['/system/ui/component/pool/EditPane'].link('current', '../pane1')

and then as you swith between panes:

db['/system/ui/component/pool/EditPane'].link('current', '../pane2')

but you will always reference the current pane by:

db['/system/ui/component/pool/EditPane/current']

Hope this makes sense.  I am going to look for opportunities in the GUI
to use this.

Regards,

-rich