#105 ADD --> ::struct::tree -exists -- myTree

[David Bigelow]

Currently there appears to be no way to detect if
a ::struct::tree name exists without usign non-lib
functions to capture what is availiable.

CURRENT METHOD:
if ![string match [info commands myTree] myTree] {
::struct::tree myTree
}

PROPOSED METHOD:
if ![::struct::tree -exists -- myTree] {
::struct::tree myTree
}

We have found, when we are using the ::struct::tree as a
central location for data (instead of arrays or lists), that
we need to verify if the tree exists before we continue
with other program logic. Since we have many procs
referencing the same ::struct::tree, and any of them
could be called at any time by the end user, we need to
check to see if the ::struct::tree exists so we make sure
to create it if it is not there.

Even though there is a way to detect if the ::struct::tree
exists using other Tcl commands - it would be easier
and more complete to have this basic call in
the ::struct::tree lib as a standard option.

Any Questions?

David Bigelow
davidhbigelow@compuserve.com

[Andreas Kupries]

Logged In: YES
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Confirming that we have nothing in the interface of tree for
checking the existence of a tree ... This is a request I
have think longer about, given that it is possible to check
for existence of the object in other ways ... Do other
object systems (like [incr Tcl], XOTcl, SNIT, ...) provide a
class method or global command to check the existence of an
object ? Or do they rely too on the introspection
capabilities of Tcl ?

[David Bigelow]

Logged In: YES
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Good point about introspection. It did not hit me about that
until I spent some time trying to figure out how to detect this
so that I could avoid trying to create something that was
already there and dealing with errors.

However, if we have the ability to destroy a tree using
the "myTree destory" - then we should be able to easily
detect it's existance within the same command set and not
have to jump to a more complicated string of commands to
determine existance (e.g., [string equal [info commands
myTree] myTree]) -- seems logical.

Any Questions?

Dave
davidhbigelow@compuserve.com